Vari-focal system having short total length

ABSTRACT

A vari-focal lens system having short total length comprising, in the order from the object side, a vari-focal subsystem consisting of a first lens unit having a positive refractive power and a second lens unit having a negative refractive power; and an imaging subsystem consisting of a third lens unit having a positive refractive power and always kept stationary, and a fourth lens unit having a positive refractive power and movable for correcting deviation of image point; said third lens unit being composed of four or a smaller number of lens elements including a positive lens element which is arranged on the object side in the third lens unit and has a convex surface on the object side, and a negative lens element, and said imaging subsystem comprising at least one aspherical surface.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a vari-focal lens system which has ashort total length, a high aperture ratio and a high vari-focal ratio,comprises four lens units and is equipped with a rear focusing means.

2. Description of the prior art

Owing to the recent progresses which have recently been made to designcompact and light-weight video cameras manufacturable at lower costs,the market of cam coders is very much activated to make the videocameras rapidly popularized among amateur photographers.

A video camera consists mainly of an electrical circuit board, anactuator system (a mechanical system) and an imaging optical system.Though attempts have hitherto been made to design the compact videocameras manufacturable at the lower costs mainly by improving theelectrical system, the imaging optical systems are now rapidly madecompacter.

Under the present circumstances, the compacter designs and reduction ofthe manufacturing costs are made by developing new vari-focal typeoptical systems through effective utilization of the progresses made inthe technologies for compacter designs of imagers, shaping ofrevolutionally symmetrical aspherical lens surface and improvement inTTL type automatic focusing.

As examples of the newly developed vari-focal type optical systems,there are known the lens systems disclosed by Japanese Patents KokaiPublication No. Sho 62-24213, Kokai Publication No. Sho 62-178917, KokaiPublication No. Sho 62-215225 and so on. However, it is limitlesslydemanded to obtain compacter and lighter lens systems, especially toshorten total lengths of lens systems and reduce diameters of the firstlens units to be used therein.

As the vari-focal lens system which is proposed before theabove-mentioned conventional examples, there is known the lens systemdisclosed by Japanese Patent Kokai Publication No. Sho 60-186818, whichis designed for a vari-focal ratio on the order of 8. This lens systemconsists, in the order from the object side, of a vari-focal subsystemcomposed of a first lens unit which is movable for focusing, a secondlens unit which has a negative refractive power and is movable forvarying focal length, and a third lens unit which has a negativerefractive power and is movable for correcting the deviation of imagepoint caused by variation of focal length; and an imaging subsystemcomposed of an aperture stop and a relay lens unit. In this lens system,the first lens unit consists, in the order from the object side, of anegative lens element, a positive lens element and a positive lenselement; the second lens unit consists, in the order from the objectside, of a negative lens element, a negative lens element and a positivelens element; and the third lens unit consists, in the order from theobject side, of a negative meniscus lens element having a stronglyconcave surface on the object side.

This lens system has a long total length and uses the first lens unitwhich has a large diameter. Further, this lens system allows remarkablevariation of spherical aberration to be caused in the vicinity of thetele position by moving the first lens unit for focusing, thereby notpermitting the first lens unit to have so strong a power. Accordingly,the point of the image formed by the first lens unit, i.e., the objectpoint for the second lens unit is far from these lens units, whereby thesecond lens unit inevitably has a weak refractive power. As a result,the second lens unit must be moved for a long distance for variation ofthe focal length of the lens system and prolongs the total length of thevari-focal subsystem. Further, since the first lens unit and the secondlens unit have the weak powers respectively, the entrance pupil is farfrom the first surface of the lens system toward the image side, therebymaking it necessary to enlarge the diameter especially of the first lensunit. Furthermore, the convex lens elements to be arranged in the firstlens unit must be thick for reserving the required thickness at themarginal portions thereof, thereby producing a vicious cycle to locatethe entrance pupil farther from the first surface of the lens system,enlarge the diameter of the first lens unit and prolong the total lengthof the vari-focal subsystem. In addition, since the lens system isfocused by moving the first lens unit, the entrance pupil is broughtstill farther from the first surface of the lens system when it isfocused on an object located at a short distance. In order to solve thisproblem related to focusing, the above-mentioned Japanese Patents KokaiPublication No. Sho 62-24213, Kokai Publication No. Sho 62-178917, KokaiPublication No. Sho 62-215225 and so on disclosed the vari-focal lenssystems of the types which adopted the rear focusing method and/or useda compensator arranged after an aperture stop. These publicationsprovided technical means very excellent for shortening total lengths ofvari-focal lens systems and reducing diameters of the first lens units.Especially, Japanese Patent Kokai Publication No. Sho 62-178917contained technical information which permits remarkably reducing numberof lens elements required for composing the lens system and correctingaberrations favorably therein by using an aspherical surface in theimaging subsystem. However, this publication scarcely made use of thistechnology effectively for designing the lens system, whereby the totallength of the lens system disclosed by this publication and the diameterof the first lens unit used in this lens system remained substantiallythe same as those of the lens system proposed previously.

Speaking concretely, the lens system disclosed by Japanese Patent KokaiPublication No. Sho 62-178917 consists of a vari-focal subsystem whichis composed of a first lens unit having a positive refractive power, anda second lens unit having a negative refractive power; and an imagingsubsystem which is composed of a third lens unit always kept stationaryand a fourth lens unit movable for correcting deviation of the imagesurface caused by variation of focal length or variation to the distanceas measured to an object to be imaged. The third lens unit of this lenssystem consists only of a single positive lens element, whereas thefourth lens unit consists of two or three lens elements including atleast one negative lens element. By adopting the rear focusing methodand using the aspherical surface, Japanese Patent Kokai Publication No.Sho 62-178917 succeeded in composing the lens system of less than 10lens elements or eliminating the unnecessary airspaces, therebyshortening the total length of the lens system and reducing the diameterof the first lens unit.

Though the lens system described above adopts the rear focusing methodso as to permit strengthening the power of the first lens unit, the lenssystem uses the first lens unit which has a power not so strong and thesecond lens unit whose power is still weak. Further, the third lens unitwhich is composed of the single lens element produces an undesirableeffect that it cannot converge a light bundle sufficiently for composingan afocal lens system and it obliges the fourth lens unit to have a longfocal length, thereby making it impossible to shorten the total lengthof the lens system and sufficiently shorten the diameter of the firstlens unit.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a vari-focallens system which comprises a vari-focal subsystem comprising a firstlens unit having a positive refractive power and a second lens unithaving a negative refractive power, and an imaging subsystem comprisinga third lens unit which has a positive refractive power and is alwayskept stationary, and a fourth lens unit which has a positive refractivepower and is movable for correcting deviation of image point caused byfocusing and variation of focal length; is designed so as to be composedof 10 or a smaller number of lens elements by selecting an adequatepower distribution among the lens elements arranged in the vari-focalsubsystem and adequate compositions for the third lens unit and thefourth lens unit respectively; has a very short total length; uses thefirst lens unit having a short diameter; and has a compact externalsize, light weight, a high aperture ratio and a high vari-focal ratio.

The vari-focal lens system having the short total length according tothe present invention comprises, in the order from the object side, thevari-focal subsystem consisting of the first lens unit having thepositive refractive power and the second lens unit having the negativerefractive power, and the imaging subsystem consisting of the third lensunit which has a positive refractive power and is always keptstationary, and the fourth lens unit which has the positive refractivepower and is movable for correcting the deviation of image point causedby variation of focal length; said third lens unit comprising a positivelens element which is arranged on the object side and has a convexsurface on the object side as well as a negative lens element having aconcave surface on the image side, and is composed of four or a smallernumber of lens elements.

It is desirable that said imaging subsystem (the third lens unit and thefourth lens unit) comprises at least one aspherical surface.

Further, the fourth lens unit comprises two or a smaller number ofpositive lens elements and the vari-focal lens system can be focused bymoving the fourth lens unit along the optical axis.

Furthermore, the vari-focal lens system according to the presentinvention, which comprises the above-mentioned four lens units includingthe third lens unit and the fourth lens unit composed as describedabove, is designed so as to satisfy the following conditions (1) through(3):

    0.55<f.sub.1 /{f.sub.T (f.sub.W ·f.sub.T).sup.1/2 }.sup.1/2 <1.35 (1)

    0.4<f.sub.III /(f.sub.W ·f.sub.T).sup.1/2 <2.5    (2)

    -0.5<HH.sub.II-III /(f.sub.W ·f.sub.T).sup.1/2 <0.25 (3)

wherein the reference symbols f_(W) and f_(T) represent focal lengths ofthe vari-focal lens system as a whole at the wide position and teleposition respectively, the reference symbol f_(I) designates the focallength of the first lens unit, the reference symbol f_(III) denotes thefocal length of the third lens unit, and the reference symbolHH_(II-III) represents the distance as measured from the principal pointof the second lens unit to the principal point of the third lens unit atthe tele position.

In the vari-focal lens system according to the present invention, thethird lens unit comprises, in the order from the object side, one tothree positive lens elements and a negative lens element having astrongly concave surface on the image side, and an object side surfaceof any one of the positive lens elements arranged in the third lens unitor any one of the lens elements arranged in the fourth lens unit isdesigned as an aspherical surface which has a curvature lowered as theportions of said surface are farther from the optical axis. It isdesirable that the third lens unit and the fourth lens unit are designedso as to satisfy the conditions (4) through (6) mentioned below:

    0.3<R.sub.31 /(N.sub.31 -1)(f.sub.W ·f.sub.T).sup.1/2 <2.0 (4)

    0.2<R.sub.36 /(N.sub.33 -1)(f.sub.W ·f.sub.T).sup.1/2 <1.6 (5)

    0.25<(D.sub.III +D.sub.IV)/(f.sub.W ·f.sub.T).sup.1/2 <1.5 (6)

wherein the reference symbol D_(III) represents thickness of the thirdlens unit as measured on the optical axis, the reference symbol D_(IV)designates thickness of the fourth lens unit as measured on the opticalaxis, the reference symbols N₃₁ and N₃₃ designate refractive indices ofthe lens elements which are arranged on the most object side and themost image side respectively in the third lens unit, and the referencesymbols R₃₁ and R₃₆ denote radii of curvature on the most object sidesurface and the most image side surface respectively of the third lensunit.

The vari-focal lens system having the short total length according tothe present invention is characterized in that it adopts the lenscomposition which comprises the vari-focal subsystem consisting, in theorder from the object side, of the first lens unit having the positiverefractive power and the second lens unit having the negative refractivepower, and the imaging subsystem consisting of the third lens unit whichhas the positive refractive power and is always kept stationary, and thefourth lens unit which has the positive refractive power and is movablefor correcting the deviation of the image surface caused mainly by thevariation of focal length and variation of the distance to an object tobe imaged; and that the refractive power of the first lens unit isremarkably strengthened, paying attention to that fact that thevari-focal lens system is not focused by moving the first lens unit andthe variation of aberrations to be caused by focusing in the vicinity ofthe tele position has little relation to the composition of the firstlens unit.

When the refractive power of the first lens unit is strengthened, thepoint of the image formed by the first lens unit, i.e., the object pointfor the second lens unit, is brought closer to the second lens unit,thereby making it possible to strengthen the refractive power of thesecond lens unit so far as the range of variation of focal length to beperformed by moving the second lens unit remains substantiallyunchanged.

Since the second lens unit of the vari-focal lens system according tothe present invention has the composition which is the same as that ofthe second lens unit of the conventional example of vari-focal lenssystem, the variations of aberrations caused by the variation of focallength are sufficiently corrected by the second lens unit itself and itis possible to suppress the variations of aberrations even when therefractive power of the second lens unit is strengthened.

By strengthening the refractive powers of the first lens unit and thesecond lens unit, it is possible to shorten the moving distance of thesecond lens unit required for the variation of focal length and shortenthe total length of the vari-focal subsystem. When the refractive powerof the first lens unit is strengthened, there may be posed a problem inconjunction with reservation of the required thickness at the marginalportion of convex lens element arranged in the first lens unit. However,since the total length of the vari-focal subsystem is shortened bystrengthening the refractive power of the first lens unit and the firstlens unit is not moved for focusing the vari-focal lens system, theentrance pupil is brought closer to the first surface of the vari-focallens system and the diameter of the first lens unit can be reduced,whereby the problem related to the thickness at the marginal portion ofthe convex lens element is solved.

It is desirable that the refractive power of the first lens unit whichis strengthened as described above satisfies the above-mentionedcondition (1).

If the first lens unit has a refractive power which is strong enough toexceed the lower limit of the condition (1), it will be impossible tocorrect spherical aberration, curvature of field and distortionsufficiently at the tele position. If the upper limit of the condition(1) is exceeded, in contrast, it will be impossible to shorten the totallength of the vari-focal lens system.

When the refractive power of the first lens unit is strengthened asdescribed above, it is desirable to define the refractive power of thesecond lens unit so as to satisfy the following condition (1'): ##EQU1##wherein the reference symbol f_(II) represents the focal length of thesecond lens unit.

If the lower limit of the condition (1') is exceeded, aberrations willtend to be varied remarkably by the variation of focal length. If theupper limit of the condition (1') is exceeded, in contrast, it will beimpossible to shorten the diameter of the first lens unit.

The technical information provided above is useful for shortening thetotal length of the vari-focal lens system by shortening the totallength of the vari-focal subsystem and is applicable to lens systemswhich have certain field angles (field angles of 36° and wider at thewide positions).

Now, description will be made on a technical concept for shortening thetotal length of the vari-focal lens system by shortening the totallength of the imaging subsystem.

The total length of the imaging subsystem is prolonged by arranging lenselements in a large number in the subsystem, reserving a wide airspacebetween the third lens unit and the fourth lens unit, and designing theimaging subsystem so as to have a back focal length longer thannecessary.

The number of the lens elements can be reduced by using an asphericalsurface, whereby the length of the lens unit comprising the asphericalsurface can be shortened.

The conventional lens system comprises a useless airspace due to thelong back focal length thereof. Generally speaking, a light bundleincident on the third lens unit is made afocal, emerges from the thirdlens unit and then falls on the fourth lens unit. The reason forallowing the afocal light bundle to fall on the fourth lens unit is toreduce the variation of spherical aberration to be caused by adjustmentof focal point. Since the afocal light bundle is incident on the fourthlens unit, the back focal length of the vari-focal lens system isdetermined by the focal length of the fourth lens unit, which in turn isdetermined by the focal length and the composition of the third lensunit. That is to say, the focal length of the fourth lens unit can beshortened by lowering the height (h) of the paraxial ray incident on thefourth lens unit. For this purpose, it is sufficient to shorten thefocal length of the second lens unit by bringing the principal point ofthe third lens unit closer to the rear principal point of the secondlens unit. The condition (2) is required for the reason described above.

If the upper limit of the condition (2) is exceeded, it will beimpossible to shorten the back focal length of the imaging subsystem. Ifthe lower limit of the condition (2) is exceeded, the light bundleemerging from the third lens unit will be strongly converged andaberrations will be remarkably varied by moving the fourth lens unit.

Further, it is desirable that a focal length f_(IV) of the fourth lensunit satisfies the following condition (2'): ##EQU2##

Since the focal length of the fourth lens unit is determined by thetotal refractive power of the first through third lens units so far asthe light bundle emerging from the third lens unit is nearly afocal, thecondition (2') can be said as a derivative condition.

If the upper limit of the condition (2') is exceeded, the back focallength of the imaging subsystem will tend to be prolonged. If the lowerlimit of the condition (2') is exceeded, the back focal length of theimaging subsystem will be shortened, thereby making it impossible toreserve the minimum airspace required for arranging an optical low passfilter and so on.

In order to shorten the back focal length of the vari-focal lens systemaccording to the present invention, it is desirable to bring theprincipal point of the third lens unit as close as possible to thesecond lens unit as described above. For this purpose, the condition (3)is adopted.

The condition (3) defines the distance as measured from the rearprincipal point of the second lens unit to the front principal point ofthe third lens unit. If the upper limit of the condition (3) isexceeded, it will be difficult to shorten the back focal length of thevari-focal lens system. If the lower limit of the condition (3) isexceeded, it will be difficult to compose the second lens unit and thethird lens unit so as to maintain favorably corrected aberrations withno mechanical interference between the second lens unit and the thirdlens unit.

When the third lens unit is composed of a single lens element as in thecase of the lens system disclosed by Japanese Patent Kokai PublicationNo. Sho 62-178917, the second lens unit and the third lens unit are aptto mechanically interfere with each other before the principal points ofthese lens units are brought close to each other. When these lens unitsare composed so as to avoid the mechanical interference, the lightbundle emerging from the third lens unit is enhanced, thereby prolongingthe back focal length of the vari-focal lens system.

By composing the third lens unit, in the order from the object side, ofone to three positive lens elements and a negative lens elements, i.e.,two to four lens elements in total, it is at least possible to bring thefront principal point of the third lens unit close to the rear principalpoint of the second lens unit, or shorten the distance between theprincipal points of the second lens unit and the third lens unit with nomechanical interference between these lens units.

From the viewpoint described above, it is desirable to design the thirdlens unit so as to satisfy the condition (2') mentioned below: ##EQU3##

The condition (3') defines the distance H_(III) as measured from thevertex of the object side surface of the third lens unit to the frontprincipal point of the third lens unit. If the upper limit of thecondition (3') is exceeded, it will be difficult to favorably correctaberrations with no mechanical interference between the second lens unitand the third lens unit while maintaining the short back focal length ofthe vari-focal lens system. If the lower limit of the condition (3') isexceeded, in contrast, each of the lens elements arranged in the thirdlens unit will have too strong a refractive power, thereby making itdifficult to correct aberrations.

For shifting the front principal point of the third lens uniteffectively toward the object side, it is desirable to design the lenselements to be used for composing the third lens unit so as to satisfythe above-mentioned conditions (4) and (5).

The conditions (4) and (5) define the powers of the most object sidesurface and the most image side surface respectively of the third lensunit. If the upper limit of the condition (4) or (5) is exceeded, itwill be difficult to shorten the distance HH_(II-III). If the lowerlimit of the condition (4) or (5) is exceeded, it will be difficult tofavorably correct spherical aberration and coma even by using anaspherical surface. The reference symbols R₃₁ and R₃₆ used in theconditions (4) and (5) represent the radii of curvature as measured inthe vicinity of the optical axis wherein the paraxial values are thesame for all the rays.

When the conditions (4) and (5) are satisfied, it is possible to obtainfavorable optical performance of the vari-focal lens system whileshortening the back focal length thereof.

The third lens unit of the vari-focal lens system according to thepresent invention comprises the lens elements in a number larger thanthat of the lens elements arranged in the third lens unit of theconventional lens system (for example, the lens system disclosed byJapanese Patent Kokai Publication No. Sho 62-178917), and is thickerthan the latter third lens unit. Therefore, the vari-focal lens systemaccording to the present invention cannot have a remarkably shortenedtotal length simply by shortening the back focal length thereof asdescribed above.

The fourth lens unit of the conventional example described abovecomprises three lens elements, whereas the fourth lens unit of thevari-focal lens system according to the present invention is composedonly of one or two positive lens elements.

It is for the purpose of correcting chromatic aberration and Petzval'ssum in the imaging subsystem as a whole that the fourth lens nit of theconventional lens system is composed of the three lens elements. Whenthe function to correct the chromatic aberration and Petzval's sum isimparted to the third lens unit which is composed of the plurality oflens elements, it is therefore possible to compose the fourth lens unitof a single lens element.

When the exit pupil of the lens system is brought too near to obtain asufficient amount of light on the light receiving surface of an imagepickup device by composing the fourth lens unit of the single lenselement, it is allowed to add a field lens (a lens element having apositive refractive power) in the vicinity of the light receivingsurface of the image pickup device or to compose the fourth lens unit oftwo positive lens elements. In the former case, the field lens may havea weak power. In the latter case, the thickness of the fourth lens unitas a whole is not increased so much and no problem is posed inconjunction with the shortening of the total length of the vari-focallens system since the fourth lens unit has a short diameter and thepower of the above-mentioned single lens element is shared between thetwo lens elements.

Furthermore, the above-mentioned condition (6) relates to the back focallength of the vari-focal lens system, and defines the total sum of thethickness of the third lens unit as a whole and that of the fourth lensunit as a whole. If the upper limit of the condition (6) is exceeded,the total sum will have a large value, thereby cancelling the effect ofshortening the back focal length for shortening the total length of thevari-focal lens system. If the lower limit of the condition (6) isexceeded, it will undesirably be difficult to reserve the requiredthickness at the marginal portion of the positive lens element.

It is desirable for further shortening the total length of thevari-focal lens system to reserve an air-space between the third lensunit and the fourth lens unit so as to satisfy the following condition(7):

    1.0×10.sup.-3 <D.sub.FT /f.sub.T .sup.2 <7.0×10.sup.-3 ( 7)

The condition (7) defines an airspace D_(FT) to be reserved between thethird lens unit and the fourth lens unit at the wide position when thevari-focal lens system is focused on an object located at infinitedistance. For accomplishing the object of the present invention, it isdesirable that D_(FT) is as narrow as possible. For focusing thevari-focal lens system, it is necessary that D_(FT) has a certain value.

On an assumption that the light bundle emerging from the third lens unitis afocal, a moving distance Δ of the fourth lens unit for focusing thevari-focal lens system on an object located at a given distance isexpressed as follows:

    Δ=a·β.sub.I-III .sup.2 ·f.sub.IV .sup.2

wherein the reference symbol β_(I-III) represents the magnification ofthe lens system composed of the first through third lens units and thereference symbol a designates a constant.

Since the moving distance is almost determined only by the focal lengthof the vari-focal lens system as a whole, the moving distance is longeras the vari-focal lens system has a longer focal length.

If the upper limit of the condition (7) is exceeded, the vari-focal lenssystem can be focused on an object located at a shorter distance, butthis is scarcely insignificant since aberrations will be aggravated whenthe vari-focal lens system is focused on the object located at theshorter distance and the airspace widened for moving the fourth lensunit for the longer distance will pose a more serious problem to prolongthe total length of the vari-focal lens system. If the lower limit ofthe condition (7) is exceeded, in contrast, it will be difficult tofocus the vari-focal lens system on an object located at a shortdistance.

Moreover, from the viewpoint to enhance optical performance of thevari-focal lens system, it is desirable to design the third lens unitand the fourth lens unit so as to satisfy the conditions (8) through(10) listed below:

    -1.8<(R.sub.31 +R.sub.32)/(R.sub.31 -R.sub.32)<-0.1        (8)

    0.2<(R.sub.35 +R.sub.36)/(R.sub.35 -R.sub.36)<3.5          (9)

    0.6<R.sub.41 /R.sub.36 <2.4                                (10)

wherein the reference symbols R₃₁ and R₃₂ represent radii of curvatureon the object side surface and the image side surface respectively ofthe lens element arranged on the most object side in the third lensunit, the reference symbols R₃₅ and R₃₆ designates the radii ofcurvature on the most object side surface and the most image sidesurface respectively of the lens element arranged on the image side inthe third lens unit, and the reference symbol R₄₁ denotes the radius ofcurvature on the most object side surface of the fourth lens unit.

The condition (8) defines a shape factor for the positive lens elementarranged on the most object side in the third lens unit. If the lowerlimit of the condition (8) is exceeded, it will be difficult to correctspherical aberration. If the upper limit of the condition (8) isexceeded, it will be impossible to design the vari-focal lens systemcompact.

The condition (9) defines a shape factor for the negative lens elementarranged on the most image side in the third lens unit. If the lowerlimit of the condition (9) is exceeded, it will be difficult to designthe vari-focal lens system compact. If the upper limit of the condition(9) is exceeded, in contrast, it will be difficult to correct sphericalaberration.

The condition (10) defines a ratio between the radius of curvature R₃₆on the most image side surface of the third lens unit and the radius ofcurvature R₄₁ on the most object side surface of the fourth lens unit.

In the airspace reserved between the third lens unit and the fourth lensunit which is variable, the light bundle is nearly afocal and sphericalaberration is scarcely varied. However, since degree of the afocalityvaries dependently on focal length, it is desirably, for minimizingvariation of focal length to be caused by focusing, that R₃₆ and R₄₁have values which are as close as possible to each other.

If the upper limit or the lower limit of the condition (10) is exceeded,not only spherical aberration but also astigmatism will easily bevaried.

When any one of the surfaces described above is designed as anaspherical surface, the radius of curvature on this surface is to bedetermined as that on the portion of the reference sphere thereoflocated in the vicinity of the optical axis wherein the paraxial valuesare the same for all the rays.

Especially for correcting spherical aberration, it is the most effectiveto use an aspherical surface as the object side surface of the positivelens element arranged in the third lens unit. However, a prettily higheffect can be obtained by using an aspherical surface as any one of thesurfaces of the fourth lens unit. An aspherical surface used in thefourth lens unit provides an effect for correcting coma rather thanspherical aberration. Accordingly, it is very effective for correctingboth aberrations to use one aspherical surface in each of the third lensunit and the fourth lens unit.

It is desirable to design the aspherical surface to be used in the thirdlens unit so as to have a curvature which is lowered as the portions ofsaid aspherical surface are farther from the optical axis. In addition,it is desirable that the degree of asphericality, i.e., departure Δxfrom the reference sphere, of the aspherical surface satisfies thefollowing conditions (11) and (12): ##EQU4## wherein the referencesymbol y represents a height as measured from the optical axis and thereference symbol y₁ is expressed as ##EQU5## (the reference symbol Fdesignates an F number of the vari-focal lens system at the wideposition).

The condition (11) defines the value of Δx of the aspherical surface aty=0.182_(y1), i.e. at the portion in the vicinity of the optical axis,and means that the departure from the reference sphere which is not solarge is desirable. Aberrations of the rays having heights within such arange can be corrected without using an aspherical surface. However, theaspherical surface having the departure from the reference sphere withinthe range defined by the condition (11) for the rays having such heightsis effective for correcting the aberrations of high orders which are tobe produced when the vari-focal lens system has a large aperture.Accordingly, it will undesirably be difficult to properly balanceaberrations if the upper limit of the condition (11) is exceeded.

For the rays having the heights above the optical axis in the vicinityof y=0.437_(y1) defined by the condition (12), it is difficult tocorrect spherical aberration and coma by using spherical lens elementsonly. Within this range of heights of rays, it is desirable to reduceamounts of aberrations to be produced by using the aspherical surfacewhich has a curvature lower than that of the reference sphere thereof.

If the lower limit of the condition (12) is exceeded, aberrations willtend to be corrected insufficiently by the aspherical surface. If theupper limit of the condition (12) is exceeded, aberrations will tend tobe aggravated.

In addition, it is desirable for correcting aberrations to design thepositive lens element having the aspherical surface in the fourth lensunit so as to satisfy the following condition:

    -1.8<(R.sub.1 +R.sub.2)/(R.sub.1 -R.sub.2)<-0.1

wherein the reference symbols R₁ and R₂ represent the radius ofcurvature of the object side surface and the radius of curvature of theimage side surface respectively, either of which is to be determined asthe paraxial radius of curvature, when the surface of interest is anaspherical surface, of the lens element having the aspherical surface inthe fourth lens unit.

This condition defines a shape factor for the positive lens elementhaving the aspherical surface in the fourth lens unit. If this conditionis not satisfied, the aspherical surface will not exhibit its effect forcorrecting aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 through FIG. 19 show sectional views illustrating compositions ofEmbodiments 1 through 19 respectively of the vari-focal lens systemaccording to the present invention;

FIG. 20, FIG. 21 and FIG. 22 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 1 of the present invention;

FIG. 23, FIG. 24 and FIG. 25 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition of the Embodiment 2 of the present invention;

FIG. 26, FIG. 27 and FIG. 28 show curves illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 3 of the present invention;

FIG. 29, FIG. 30 and FIG. 31 show curves illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 4 of the present invention;

FIG. 32, FIG. 33 and FIG. 34 show graphs visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 5 of the present invention;

FIG. 35, FIG. 36 and FIG. 37 show curves visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 6 of the present invention;

FIG. 38, FIG. 39 and FIG. 40 show graphs illustrating aberrationcharacteristics at the wide position, intermediate foal length and teleposition respectively of the Embodiment 7 of the present invention;

FIG. 41, FIG. 42 and FIG. 43 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 8 of the present invention;

FIG. 44, FIG. 45 and FIG. 46 show curves illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 9 of the present invention;

FIG. 47, FIG. 48 and FIG. 49 show graphs visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 10 of the present invention;

FIG. 50, FIG. 51 and FIG. 52 show curves visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 11 of the present invention;

FIG. 53, FIG. 54 and FIG. 55 show graphs visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 12 of the present invention;

FIG. 56, FIG. 57 and FIG. 58 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 13 of the present invention;

FIG. 59, FIG. 60 and FIG. 61 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 14 of the present invention;

FIG. 62, FIG. 63 and FIG. 64 show curves visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 15 of the present invention;

FIG. 65, FIG. 66 and FIG. 67 show curves illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 16 of the present invention;

FIG. 68 shows graphs illustrating aberration characteristics at the teleposition of the Embodiment 16 of the present invention when it isfocused on an object located at a short distance;

FIG. 69, FIG. 70 and FIG. 71 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 17 of the present invention whenit is focused on an object located an infinite distance;

FIG. 72 shows curves illustrating aberration characteristics at the teleposition of the Embodiment 17 of the present invention when it isfocused on an object located at a short distance;

FIG. 73, FIG. 74 and FIG. 75 show curves visualizing aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 18 of the present invention whenit is focused on an object located at infinite distance;

FIG. 76 shows curves illustrating aberration characteristics at the teleposition of the Embodiment 18 of the present invention when it isfocused on an object located at a short distance;

FIG. 77, FIG. 78 and FIG. 79 show graphs illustrating aberrationcharacteristics at the wide position, intermediate focal length and teleposition respectively of the Embodiment 19 of the present invention whenit is focused on an object located at infinite distance; and

FIG. 80 shows curves visualizing aberration characteristics at the teleposition of the Embodiment 19 of the present invention when it isfocused on an object located at a short distance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the vari-focal lens system having the short total length accordingto the present invention will be described more detailedly below withreference to the preferred embodiments thereof illustrated in theaccompanying drawings and given in the form of the following numericaldata:

    ______________________________________                                        Embodiment 1                                                                  f = 8.76˜65.96,                                                                            f/2.0˜f/2.6                                          2ω = 50.2°˜7.2°                                     r.sub.1 = 51.4795                                                                         d.sub.1 = 1.0000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 23.9639                                                                         d.sub.2 = 5.6000                                                                          n.sub.2 =- 1.60311                                                                       ν.sub.2 = 60.70                         r.sub.3 = -71.1147                                                                        d.sub.3 = 1.1500                                                  r.sub.4 = 17.8414                                                                         d.sub.4 = 3.8000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 33.3216                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 37.2001                                                                         d.sub.6 = 1.1026                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.3340                                                                          d.sub.7 = 2.0000                                                  r.sub.8 = -10.3299                                                                        d.sub.8 = 1.0000                                                                          n.sub.5 = 1.69680                                                                        ν.sub.5  = 55.52                        r.sub.9 = 9.5724                                                                          d.sub.9 = 2.0000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 469.3178                                                                       d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 7.9854                                                             (aspherical surface)                                                                      d.sub.12 = 3.5000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -37.1999                                                                       d.sub.13 = 1.8644                                                 r.sub.14 = 42.6275                                                                        d.sub.14 = 1.2104                                                                         n.sub.8 = 1.80518                                                                        ν.sub.8 = 25.43                         r.sub.15 = 6.7517                                                                         d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 10.1365                                                            (aspherical surface)                                                                      d.sub.16 = 3.3000                                                                         n.sub.9 = 1.56384                                                                        ν.sub.9 = 60.69                         r.sub.17 = -33.5763                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18  = 5.1000                                                                        n.sub.10 = 1.54771                                                                       ν.sub.10 = 62.83                        r.sub.19 = ∞                                                                        d.sub.19 = 1.2100                                                 r.sub.20 = ∞                                                                        d.sub.20 = 0.6000                                                                         n.sub.11 = 1.48749                                                                       ν.sub.11 = 70.20                        r.sub.21 = ∞                                                            aspherical surface coefficient                                                (12th surface)                                                                A.sub.4 = -0.25435 × 10.sup.-3, A.sub.6 = -0.144404 ×             10.sup.|5                                                            A.sub.8 = -0.46594 × 10.sup.-7 P = 1                                    (16th surface)                                                                A.sub.4 = -0.22509 × 10.sup.-3, A.sub.6 = 0.35300                       × 10.sup.-5                                                             G = -0.91309 × 10.sup.-7                                                f       8.76           24.04   65.96                                          D.sub.1 1.000          9.497   15.916                                         D.sub.2 15.916         7.420   1.000                                          D.sub.3 6.391          3.500   11.458                                         D.sub.4 7.067          9.958   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.753, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.296                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 0.855, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.591                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.142, H.sub.III       /(f.sub.W · f.sub.T).sup.1/2 = -0.358                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.477         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.335         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.394, D.sub.FT          /f.sub.T.sup.2 = 2.634 × 10.sup.-3                                      (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.647                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.376, R.sub.41 /R.sub.36 =     1.501                                                                         total length of lens system 63.320                                            diameter of front lens component 25.2φ                                    Embodiment 2                                                                  f = 6.49˜48.90,                                                                            F/1.4˜F/2.2                                          2ω = 51.8°˜7.4°                                     r.sub.1 = 57.3585                                                                         d.sub.1 = 1.0000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 23.7370                                                                         d.sub.2 = 5.6000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -71.5301                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 17.1706                                                                         d.sub.4 = 3.8000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 43.6355                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 1140.8303                                                                       d.sub.6 = 1.1026                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 6.8647                                                                          d.sub.7 = 2.0000                                                  r.sub.8 = -9.8125                                                                         d.sub.8 =  1.0000                                                                         n.sub.5 = 1.69680                                                                        ν.sub.5 =]55.52                         r.sub.9 = 8.1232                                                                          d.sub.9 = 2.600                                                                           n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 735.9093                                                                       d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 13.4774                                                                        d.sub.12 = 3.400                                                                          n.sub.7 = 1.60311                                                                        ν.sub.7 = 60.70                         r.sub.13 = -65.0959                                                                       d.sub.13 = 0.3000                                                 r.sub.14 = 16.4183                                                                        d.sub.14 = 2.5000                                                                         n.sub.8 = 1.60311                                                                        ν.sub.8 = 60.70                         r.sub.15 = 141.9059                                                                       d.sub.15 = 0.3000                                                 r.sub.16 = 8.6800                                                                         d.sub.16 = 2.4000                                                                         n.sub.9 = 1.60311                                                                        ν.sub.9 = 60.70                         r.sub.17 = 17.8996                                                                        d.sub.17 = 0.7000                                                 r.sub.18 = -28.6777                                                                       d.sub.18  = 1.2104                                                                        n.sub.10 = 1.80518                                                                       ν.sub.10 = 25.43                        r.sub.19 = 8.6110                                                                         d.sub.19 = D.sub.3                                                            (variable)                                                        r.sub.20 = 8.9305                                                             (aspherical surface)                                                                      d.sub.20 = 3.3000                                                                         n.sub.11 = 1.56384                                                                       ν.sub.11 = 60.69                        r.sub.21 = -18.5051                                                                       d.sub.21 = D.sub.4                                                            (variable)                                                        r.sub.22 = ∞                                                                        d.sub.22 = 5.1000                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.23 = ∞                                                                        d.sub.23 = 1.2100                                                 r.sub.24 = ∞                                                                        d.sub.24 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.25 = ∞                                                            aspherical surface coefficient                                                A.sub.4 = -0.37686 × 10.sup.-3, A.sub.6 = -0.16869                      × 10.sup.-5                                                             A.sub.8 = 0 P = 1                                                             f       6.49           17.82   48.90                                          D.sub. 1                                                                              1.000          9.287   14.619                                         D.sub.2 14.619         6.332   1.000                                          D.sub.3 6.351          3.500   6.931                                          D.sub.4 2.580          5.431   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.940, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.329                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 0.836, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.627                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.120, H.sub.III       /(f.sub.W · f.sub.T).sup.1/2 = -0.442                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.254         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.600         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.792, D.sub.FT          /f.sub.T.sup.2 = 2.899 × 10.sup.-3                                      (R.sub.31  + R.sub.32)/(R.sub.31 - R.sub.32) = -0.657                         (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.538, R.sub.41 /R.sub.36 =     1.037                                                                         total length of lens system 63.332                                            diameter of front lens component 24.0φ                                    Embodiment 3                                                                  f = 6.49˜48.90,                                                                            F/1.4˜F/2.2                                          2ω = 51.8°˜7.4°                                     r.sub.1 = 49.2800                                                                         d.sub.1 = 1.0000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 23.1954                                                                         d.sub.2 = 5.2000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -1.04.9168                                                                      d.sub.3 = 0.1500                                                  r.sub.4 = 18.4142                                                                         d.sub.4 = 3.7500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 58.6398                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 60.7724                                                                         d.sub.6 = 1.1026                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 6.6301                                                                          d.sub.7 = 2.0000                                                  r.sub.8 = -9.8199                                                                         d.sub.8 = 1.0000                                                                          n.sub.5 = 1.69680                                                                        ν.sub.5 = 55.52                         r.sub.9 = 11.1626                                                                         d.sub.9 = 2.4000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = -73.9440                                                                       d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 8.9570                                                                         d.sub.12 = 4.2000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -97.9282                                                                       d.sub.13 = 0.8990                                                 r.sub.14 = -18.4246                                                                       d.sub.14 = 1.2000                                                                         n.sub.8 = 1.80518                                                                        ν.sub.8 = 25.43                         r.sub.15 = 9.9456                                                                         d.sub.15 = 0.5000                                                 r.sub.16 =  16.4456                                                                       d.sub.16 = 2.4000                                                                         n.sub.9 = 1.69680                                                                        ν.sub.9 = 55.52                         r.sub.17 = -31.7035                                                                       d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 9.9286                                                             (aspherical surface)                                                                      d.sub.18 = 4.1000                                                                         n.sub.10 = 1.56384                                                                       ν.sub.10 = 60.69                        r.sub.19 = -29.2366                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 5.1000                                                                         n.sub.11 = 1.54771                                                                       ν.sub.11 = 62.83                        r.sub.21 = ∞                                                                        d.sub.21 = 1.2100                                                 r.sub.22 = ∞                                                                        d.sub.22 = 0.6000/ n.sub.12 = 1.48749                                                     ν.sub.12 = 70.20                                   r.sub.23 = ∞                                                            aspherical surface coefficient                                                A.sub.4 = -0.22999 × 10.sup.-3, A.sub.6 = -0.977968 ×             10.sup.-6                                                                     A.sub.8 = 0 P = 1                                                             f        6.49          17.82   48.90                                          D.sub.1 1.300          9.552   14.895                                         D.sub.2 15.095         6.843   1.500                                          D.sub.3 3.764          2.500   7.591                                          D.sub.4 6.264          7.528   2.437                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.941, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.380                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 1.427, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.767                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.200, H.sub.III       /(f.sub.W · f.sub.T).sup.1/2 = -0.159                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.722         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.693         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.747, D.sub.FT          /f.sub.T.sup.2 = 3.175 ×  10.sup.-3                                     (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.832                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.299,                          total length of lens system 62.743                                            diameter of front lens component 26.0φ                                    Embodiment 4                                                                  f = 6.49˜48.89,                                                                            F/1.5˜F/2.1                                          2ω = 51.8°˜7.4°                                     r.sub.1 = 61.1461                                                                         d.sub.1 = 1.0000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 25.5792                                                                         d.sub.2 = 5.2000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -82.8557                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 18.9721                                                                         d.sub.4 = 3.7500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 50.8855                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 293.8083                                                                        d.sub.6 =  1.1026                                                                         n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.3631                                                                          d.sub.7 = 2.0000                                                  r.sub.8 = -10.8606                                                                        d.sub.8 = 1.0000                                                                          n.sub.5 = 1.69680                                                                        ν.sub.5 = 55.52                         r.sub.9 = 9.0391                                                                          d.sub.9 = 2.4000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = -479.7696                                                                      d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 11.1400                                                                        d.sub.12 = 4.2000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -43.8310                                                                       d.sub.13 = 0.3000                                                 r.sub.14 = 8.2915                                                                         d.sub.14 = 2.4000                                                                         n.sub.8 = 1.69680                                                                        ν.sub.8 = 55.52                         r.sub.15 = 19.0091                                                                        d.sub.15 = 0.6044                                                 r.sub.16 = -27.4999                                                                       d.sub.16 = 1.2104                                                                         n.sub.9 = 1.80518                                                                        ν.sub.9 = 25.43                         r.sub.17 = 7.3325                                                                         d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 9.6114                                                             (aspherical surface)                                                                      d.sub.18 4.1000                                                                           n.sub.10 = 1.56384                                                                       ν.sub.10 = 60.69                        r.sub.19 = -15.3541                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 5.1000                                                                         n.sub.11 = 1.54771                                                                       ν.sub.11 = 62.83                        r.sub.21 = ∞                                                                        d.sub.21 = 1.2100                                                 r.sub.22 = ∞                                                                        d.sub.22 = 0.6000                                                                         n.sub.12 = 1.48749                                                                       ν.sub.12 = 70.20                        r.sub.23 = ∞                                                            aspherical surface coefficient                                                A.sub.4 = -0.39357 × 10.sup.-3, A.sub.6 = -0.40862                      × 10.sup.-6                                                             A.sub.8 = 0 P = 1                                                             f       6.49           17.82   48.89                                          D.sub.1 1.300          10.119  16.488                                         D.sub.2 16.688         7.869   1.500                                          D.sub.3 4.934          2.472   6.157                                          D.sub.4 3.660          6.123   2.437                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.026, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.374                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 1.025, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.626                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.205, H.sub.III       /(f.sub.W · f.sub.T).sup.1/2 = -0.555                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.898         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.511         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.719, D.sub.FT          /f.sub.T.sup.2 = 2.576 × 10.sup.-3                                      (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.595                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.579, R.sub.41 /R.sub.36 =     1.311                                                                         total length of lens system 62.418                                            diameter of front lens component 24.0φ                                    Embodiment 5                                                                  f = 6.49˜48.90,                                                                            F/1.6˜F/2.2                                          2ω = 51.8°˜7.4°                                     r.sub.1 = 62.6591                                                                         d.sub.1 = 1.0000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 25.6867                                                                         d.sub.2 = 5.2000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -88.1045                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 19.1934                                                                         d.sub.4 = 3.7500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 58.7953                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = -157.6505                                                                       d.sub.6 = 1.1026                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.6914                                                                          d.sub.7 = 2.0000                                                  r.sub.8 = -13.7250                                                                        d.sub.8 = 1.0000                                                                          n.sub.5 = 1.69680                                                                        ν.sub.5 = 55.52                         r.sub.9 = 8.3911                                                                          d.sub.9 = 2.4000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 204.9580                                                                       d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 11.4645                                                                        d.sub.12 = 4.2000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -41.1109                                                                       d.sub.13 = 0.3000                                                 r.sub.14 = 9.3876                                                                         d.sub.14 = 2.4000                                                                         n.sub.8 = 1.69680                                                                        ν.sub.8 = 55.52                         r.sub.15 = 28.3293                                                                        d.sub.15 = 0.4948                                                 r.sub.16 =  -24.6734                                                                      d.sub.16 = 1.2104                                                                         n.sub.9 = 1.80518                                                                        ν.sub.9 = 25.43                         r.sub.17 = 8.4053                                                                         d.sub.17 = D.sub.3 (variable)                                     r.sub.18 = 24.2967                                                                        d.sub.18 = 2.0000                                                                         n.sub.10 = 1.60311                                                                       ν.sub.10 = 60.70                        r.sub.19 = -36.3424                                                                       d.sub.19 = 0.1000                                                 r.sub.20 = 10.7865                                                            (aspherical surface)                                                                      d.sub.20 = 2.000                                                                          n.sub.11 = 1.60311                                                                       ν.sub.11 = 60.70                        r.sub.21 = 70.0000                                                                        d.sub.21 = D.sub.4                                                            (variable)                                                        r.sub.22 = ∞                                                                        d.sub.22 = 5.1000                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.23 = ∞                                                                        d.sub.23 = 1.2100                                                 r.sub.24 = ∞                                                                        d.sub.24 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.25 = ∞                                                            aspherical surface coefficient                                                A.sub.4 = -0.17524 × 10.sup.-3, A.sub.6 = -0.70866                      × 10.sup.-5                                                             A.sub.8 = -0.23328 × 10.sup.6 P = 1                                     f       6.49           17.82   48.90                                          D.sub.1 1.300          10.352  16.336                                         D.sub.2 16.536         7.483   1.500                                          D.sub.3 5.837          3.797   7.805                                          D.sub.4 3.467          5.507   1.500                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.015, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.387                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 1.043, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.641                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.125, H.sub.III       /(f.sub.W · f.sub.T).sup.1/2 = -0.475                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.924         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.586         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.713, D.sub.FT          /f.sub.T.sup.2 = 3.264 × 10.sup.-3                                      (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.564                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.492, R.sub.41 /R.sub.36 =     2.891                                                                         total length of lens system 62.866                                            diameter of front lens component 24.7φ                                    Embodiment 6                                                                  f = 6.900˜38.800,                                                                          F/1.45˜F/2.23                                        2ω = 49.0°˜9.2°                                     r.sub.1 = 46.6262                                                                         d.sub.1 = 1.1000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 21.8337                                                                         d.sub.2 = 4.6000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -53.5341                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 14.4337                                                                         d.sub.4 = 2.9000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 33.8040                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = -152.2103                                                                       d.sub.6 = 0.9000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 6.5436                                                                          d.sub.7 = 2.3000                                                  r.sub.8 = -9.8267                                                                         d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 8.4818                                                                          d.sub.9 = 1.9000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 45.4524                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.7000                                                 r.sub.12 = 10.0679                                                            (aspherical surface)                                                                      d.sub.12 = 3.6000                                                                         n.sub.7 = 1.58913                                                                        ν.sub.7 = 60.97                         r.sub.13 = - 62.2959                                                                      d.sub.13 = 0.1500                                                 r.sub.14 = 8.9432                                                                         d.sub.14 = 4.0000                                                                         n.sub.8 = 1.72000                                                                        ν.sub.8 = 50.25                         r.sub.15 = -71.7917                                                                       d.sub.15 = 0.1500                                                 r.sub.16 = -202.7666                                                                      d.sub.16 = 0.8000                                                                         n.sub.9 = 1.80518                                                                        ν.sub.9 = 25.43                         r.sub.17 = 5.4043                                                                         d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 7.7606                                                             (aspherical surface)                                                                      d.sub.18 = 3.3000                                                                         n.sub.10 = 1.58913                                                                       ν.sub.10 = 60.97                        r.sub.19 = -41.3529                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 6.0000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        r.sub.21 = ∞                                                            aspherical surface coefficient                                                (12th surface)                                                                P = 1.0000, A.sub.4 = -0.15714 × 10.sup.|3                     A.sub.6 = -0.18163 ×  10.sup.-5, A.sub.8 = 0.70381                      × 10.sup.-8                                                             (18th surface)                                                                P = 1.0000, A.sub.4 = -0.22486 × 10.sup.-3                              A.sub.6 = -0.50608 × 10.sup.-5, A.sub.8 = 0.27776 × 10.sup.31     f       6.900          16.362  38.800                                         D.sub.1 0.900          6.827   11.236                                         D.sub.2 11.636         5.708   1.300                                          D.sub.3 4.465          2.700   5.987                                          D.sub.4 3.521          5.287   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.922, f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.344                f.sub.III (f.sub.W · f.sub.T).sup.1/2  = 0.864, f.sub.IV             (f.sub.W · f.sub.T).sup.1/2  = 0.695                                 HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2 = -0.0373, H.sub.III      /(f.sub.W · f.sub.T).sup.1/2 = -0.395                                R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.044         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.410         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.733, D.sub.FT          /f.sub.T.sup.2 = 3.977 × 10.sup.-3                                      (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.722                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.948, R.sub.41 /R.sub.36 =     1.436                                                                         total length of lens system 52.959                                            diameter of front lens component 21.0φ                                    Embodiment 7                                                                  f = 6.900˜38.799,                                                                          F/1.44˜F/2.17                                        2ω = 49.0°˜9.2°                                     r.sub.1 = 33.6905                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 20.4286                                                                         d.sub.2 = 4.4000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 =  60.70                        r.sub.3 = -283.3472                                                                       d.sub.3 = 0.1500                                                  r.sub.4 = 20.9192                                                                         d.sub.4 = 3.1000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 70.1720                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 107.1270                                                                        d.sub.6 = 0.8000                                                                          n.sub.4 = 1.80610                                                                        ν.sub.4 = 40.95                         r.sub.7 = 5.7148                                                                          d.sub.7 = 2.2000                                                  r.sub.8 = -8.3221                                                                         d.sub.8 = 0.7000                                                                          n.sub.5 = 1.60738                                                                        ν.sub.5 = 56.81                         r.sub.9 = 7.8205                                                                          d.sub.9 = 2.1000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = -126.6923                                                                      d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 9.2402                                                             (aspherical surface)                                                                      d.sub.12 = 3.8000                                                                         n.sub.7 =  1.58913                                                                       ν.sub.7 = 60.97                         r.sub.13 = -62.7605                                                                       d.sub.13 = 0.1500                                                 r.sub.14 = 9.0124                                                                         d.sub.14 = 4.1000                                                                         n.sub.8 = 1.58913                                                                        ν.sub.8 = 60.97                         r.sub.15 = -69.0295                                                                       d.sub.15 = 0.1500                                                 r.sub.16 = 26.1836                                                                        d.sub.16 = 0.8000                                                                         n.sub.9 = 1.84666                                                                        ν.sub.9 = 23.78                         r.sub.17 = 5.1686                                                                         d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 6.7364                                                             (aspherical surface)                                                                      d.sub.18 = 4.0000                                                                         n.sub.10 = 1.48749                                                                       ν.sub.10 = 70.20                        r.sub.19 = -21.1553                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                            r.sub.21 = ∞                                                                        d.sub.20 = 6.0000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        aspherical surface coefficient                                                (12th surface)                                                                P = 1.0000, A.sub.4 = -0.25905 ×  10.sup.-3                             A.sub.6 = -0.23436 × 10.sup.-5, A.sub.8 = 0.62261                       × 10.sup.-8                                                             (18th surface)                                                                P = 1.0000, A.sub.4 = -0.39540 × 10.sup.-3                              A.sub.6 = -0.69335 × 10.sup.-5, A.sub.8 = -0.11826                      × 10.sup.-7                                                             f       6.900          16.362  38.799                                         D.sub.1 0.600          9.340   15.258                                         D.sub.2 0.329          3.958   1.000                                          D.sub.3 4.044          2.500   5.508                                          D.sub.4 3.464          5.008   2.000                                          f.sub.1 /{f.sub.t (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.126,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.351                       f.sub.III /(f.sub.W · f.sub.T).sup.1/2  = 0.798,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.672                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = 0.0118,                H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.351                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2 = 0.959          R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.373         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2  = 0.794,                  D.sub.FT /f.sub.T.sup.2 = 0.3659 × 10.sup.-3                            (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.743                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.492,                          R.sub.41 /R.sub.36 = 1.303                                                    total length of lens system 49.669                                            diameter of front lens component 21.7φ                                    Embodiment 8                                                                  f = 6.900˜38.800,                                                                          F/1.44˜F/2.04                                        2ω = 49.0°˜9.2°                                     r.sub.1 = 41.7937                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 22.8622                                                                         d.sub.2 =  4.1000                                                                         n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -118.8556                                                                       d.sub.3 = 0.2000                                                  r.sub.4 = 19.1412                                                                         d.sub.4 = 3.000                                                                           n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 73.3694                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 80.3217                                                                         d.sub.6 = 0.9000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.7697                                                                          d.sub.7 = 2.8000                                                  r.sub.8 = -11.2903                                                                        d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 10.5774                                                                         d.sub.9 = 2.000                                                                           n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 37.1339                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.7000                                                 r.sub.12 = 7.9500                                                                         d.sub.12 = 4.6000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -30.1367                                                                       d.sub.13 = 0.2000                                                 r.sub.14 = 29.2800                                                                        d.sub.14 = 3.7303                                                                         n.sub.8 = 1.84666                                                                        ν.sub.8 = 23.78                         r.sub.15 = 6.0792                                                                         d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 7.5823                                                             (aspherical surface)                                                                      d.sub.16 = 3.1000                                                                         n.sub.9 = 1.60311                                                                        ν.sub.9 = 60.70                         r.sub.17 = -32.4893                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 6.0000                                                                         n.sub.10 = 1.51633                                                                       ν.sub.10 = 64.15                        r.sub.19 = ∞                                                            aspherical surface coefficient                                                (12th surface)                                                                P = 1.0000, A.sub.4 = -0.25835 × 10.sup.-3                              A.sub.6 = -0.30075 × 10.sup.-5, A.sub.8 = -0.32127 × 10.sup.      -7                                                                            (16th surface)                                                                P = 1.0000, A.sub.4 = -0.36853 × 10.sup.-3                              A.sub.6 = 0.74935 × 10.sup.-5, A.sub.8 = -0.52612                       × 10.sup.-6                                                             f       6.900          16.362  38.800                                         D.sub.1 0.600          7.480   12.823                                         D.sub.2 13.523         6.644   1.300                                          D.sub.3 3.589          2.200   5.481                                          D.sub.4 3.892          5.281   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.054,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.412                       f.sub.III /(f.sub.W · f.sub.T).sup.1/2 = 1.034,                      f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.642                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.1580,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.514                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.697         R.sub. 36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.439        D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2  = 0.711,                  D.sub.FT /f.sub.T.sup.2 = 3.641 × 10.sup.-3                             (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.583                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.524,                          R.sub.41 /R.sub.36 = 1.247                                                    total length of lens system 54.023                                            diameter of front lens component 21.5φ                                    Embodiment 9                                                                  f = 6.900˜38.800,                                                                          F/2.06˜F/2.05                                        2ω = 49.0°˜9.2°                                     r.sub.1 = 49.0000                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 24.6210                                                                         d.sub.2 = 4.1000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -87.7864                                                                        d.sub.3  = 0.2000                                                 r.sub.4 = 17.6736                                                                         d.sub.4 = 3.2000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 58.6771                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 151.1492                                                                        d.sub.6 = 0.9000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.1029                                                                          d.sub.7 = 2.6500                                                  r.sub.8 = -11.0922                                                                        d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 10.2657                                                                         d.sub.9 = 1.8000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 94.4742                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.7000                                                 r.sub.12 = 6.3725                                                             (aspherical surface)                                                                      d.sub.12 = 3.1500                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 =  -50.1345                                                                      d.sub.13 = 0.1500                                                 r.sub.14 = 27.7421                                                                        d.sub.14 = 2.7421                                                                         n.sub.8 = 1.84666                                                                        ν.sub.8 = 23.78                         r.sub.15 = 5.0177                                                                         d.sub.15 = D.sub.                                                             (variable)                                                        r.sub.16 = 7.8414                                                                         d.sub.16 = 3.4000                                                                         n.sub.9 = 1.60311                                                                        ν.sub.9 = 60.70                         (aspherical surface)                                                          r.sub.17 = -22.6625                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 6.0000                                                                         n.sub.10 = 1.51633                                                                       ν.sub.10 = 64.15                        r.sub.19 = ∞                                                            aspherical surface coefficient                                                (12th surface)                                                                P = 1.0000, A.sub.4 = -0.36365 × 10.sup.-3                              A.sub.6 = -0.66028 × 10.sup.-5, A.sub.8 = -0.14291                      × 10.sup.-6                                                             (16th surface)                                                                P = 1.0000, A.sub.4 = -0.27343 × 10.sup.-3                              A.sub.6 =  -0.85428 × 10.sup.-5, A.sub.8 = 0.23185                      × 10.sup.-6                                                             f       6.900          16.362  38.800                                         D.sub.1 0.700          7.606   13.000                                         D.sub.2 13.600         6.694   1.300                                          D.sub.3 3.885          2.800   6.580                                          D.sub.4 4.696          5.780   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.039,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.429                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.255,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.616                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.2257,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.603                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.559         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.362         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.577,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.774                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.438,                          R.sub.41 /R.sub.36 = 1.563                                                    total length of lens system 52.959                                            diameter of front lens component 21.4φ                                    Embodiment 10                                                                 f = 6.900˜38.800,                                                                          F/1.41˜F/1.99                                        2ω = 49.0°˜9.2°                                     r.sub.1 = 43.0767                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 19.5560                                                                         d.sub.2 = 4.2000                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -600.3543                                                                       d.sub.3 = 0.1500                                                  r.sub.4 = 20.8028                                                                         d.sub.4 = 3.3000                                                                          n.sub.3 = 1.65844                                                                        ν.sub. 3 = 50.86                        r.sub.5 = 127.7478                                                                        d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 40.8164                                                                         d.sub.6 = 0.8000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 6.1997                                                                          d.sub.7 = 2.3000                                                  r.sub.8 = -8.3248                                                                         d.sub.8 = 0.7000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 8.9835                                                                          d.sub.9 = 2.0000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 86.3663                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 8.2684                                                                         d.sub.12 = 4.6000                                                                         n.sub.7 ≦ 1.58913                                                                 ν.sub.7 = 60.97                         r.sub.13 = -15.6514                                                                       d.sub.13 = 0.1500                                                 r.sub.14 = 54.7313                                                                        d.sub.14 = 5.0896                                                                         n.sub.8  = 1.84666                                                                       ν.sub.8 = 23.78                         r.sub.15 = 7.8285                                                                         d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 7.0945                                                             (aspherical surface)                                                                      d.sub.16 = 4.0000                                                                         n.sub.9 = 1.48749                                                                        ν.sub.9 = 70.20                         r.sub.17 = -11.6664                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 6.0000                                                                         n.sub.10 = 1.51633                                                                       ν.sub.10 = 64.15                        r.sub.19 = ∞                                                            Aspherical surface coefficient                                                (12th surface)                                                                P = 1.0000, A.sub.4 = -0.40016 × 10.sup.-3                              A.sub.6 = -0.17286 × 10.sup.-5, A.sub.8 = -0.37067                      × 10.sup.-7                                                             (16th surface)                                                                P = 1.0000, A.sub.4 = -0.69721 × 10.sup.-3                              A.sub.6 = -0.33798 × 10.sup.-5, A.sub.8 = -0.37651                      × 10.sup.-6                                                             f       6.900           16.362 38.800                                         D.sub.1 0.600          9.406   15.230                                         D.sub.2 8.315          3.911   1.000                                          D.sub.3 3.459          2.500   5.959                                          D.sub.4 4.501          5.459   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.121,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.378                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 0.975,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.595                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.0901,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.413                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.858         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.565         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.846,                   D.sub.FT f.sub.T.sup.2 = 3.958 × 10.sup. -3                             (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.309                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.334,                          R.sub.41 /R.sub.36 = 0.906                                                    total length of lens system 50.953                                            diameter of front lens component 21.0φ                                    Embodiment 11                                                                 f = 6.700˜50.440,                                                                          F/1.44˜F/2.11                                        2ω = 50.4°˜7.2°                                     r.sub.1 = 53.9356                                                                         d.sub.1 = 1.5000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 28.6454                                                                         d.sub.2 = 4.8000                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = -103.6510                                                                       d.sub.3 = 0.1500                                                  r.sub.4 = 20.9530                                                                         d.sub.4 = 3.4500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 55.3350                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 =  35.1277                                                                        d.sub.6 = 1.1000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.6963                                                                          d.sub.7 = 2.9000                                                  r.sub.8 = -9.8110                                                                         d.sub.8 = 1.0000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 12.3932                                                                         d.sub.9 = 2.0000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 99.8484                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 13.9316                                                            (aspherical surface)                                                                      d.sub.12 = 3.5000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = -51.9617                                                                       d.sub.13 = 0.2000                                                 r.sub.14 = 11.2530                                                                        d.sub.14 = 2.5000                                                                         n.sub.8 = 1.60311                                                                        ν.sub.8 = 60.70                         r.sub.15 = 30.6895                                                                        d.sub.15 = 0.6200                                                 r.sub.16 = -192.3609                                                                      d.sub.16 = 1.2100                                                                         n.sub.9 = 1.84666                                                                        ν.sub.9 = 23.78                         r.sub.17 = 11.1804                                                                        d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 12.3060                                                            (aspherical surface)                                                                      d.sub.18 = 3.3000                                                                         n.sub.10 = 1.56873                                                                       ν.sub.10 = 63.16                        r.sub.19 = -20.0283                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 1.0000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        r.sub.21 = ∞                                                                        d.sub.21 = 0.7000                                                 r.sub.22 = ∞                                                                        d.sub.22 = 5.8600                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.23 = ∞                                                                        d.sub.23 = 1.2100                                                 r.sub.24 = ∞                                                                        d.sub.24 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.25  = ∞                                                           aspherical surface coefficient                                                (12th surface)                                                                P = 0.5388, A.sub.4 = -0.10978 × 10.sup.-4                              A.sub.6 = -0.48118 × 10.sup.-7                                          (18th surface)                                                                P = 0.6118, A.sub.4 = -0.22709 × 10.sup.-3                              A.sub.6 = 0.40034 × 10.sup.-7                                           f       6.700          18.383  50.440                                         D.sub.1 0.700          10.815  18.075                                         D.sub.2 18.875         8.760   1.500                                          D.sub.3 4.812          2.591   6.626                                          D.sub.4 3.503          5.724   1.690                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.108,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.420                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.144,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.757                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.0114,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  =  -0.345                    R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.088         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.718         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.616,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.577                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.890,                          R.sub.41 /R.sub.36 = 1.101                                                    total length of lens system 64.957                                            diameter of front lens component 24.3φ                                    Embodiment 12                                                                 f = 6.700˜50.440,                                                                          F/1.43˜F/2.26                                        2ω = 50.4°˜7.2°                                     r.sub.1 = 48.9885                                                                         d.sub.1 = 1.5000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 24.8892                                                                         d.sub.2 = 4.5000                                                                          n.sub. 2 = 1.60311                                                                       ν.sub.2 = 60.70                         r.sub.3 = -377.4066                                                                       d.sub.3 = 0.1500                                                  r.sub.4 = 23.4540                                                                         d.sub.4 = 3.4000                                                                          n.sub.3 = 1.63854                                                                        ν.sub.3 = 55.38                         r.sub.5 = 100.3216                                                                        d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 104.0635                                                                        d.sub.6 = 1.1000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.2555                                                                          d.sub.7 = 2.6000                                                  r.sub.8 = -9.8423                                                                         d.sub.8 = 1.0000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 10.3952                                                                         d.sub.9 = 2.0000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 95.3109                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 11.7960                                                            (aspherical surface)                                                                      d.sub.12 = 4.0000                                                                         n.sub.7 = 1.60311                                                                        ν.sub.7 = 60.70                         r.sub.13 = -33.4377                                                                       d.sub.13 = 0.2000                                                 r.sub.14 = 11.0871                                                                        d.sub.14 = 2.6500                                                                         n.sub.8 = 1.56873                                                                        ν.sub.8 = 63.16                         r.sub.15 = 33.0044                                                                        d.sub.15 = 0.3500                                                 r.sub.16 = 106.7443                                                                       d.sub.16 = 0.9000                                                                         n.sub.9 = 1.84666                                                                        ν.sub.9 = 23.78                         r.sub.17 = 10.3881                                                                        d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 13.2932                                                                        d.sub.18 = 3.1000                                                                         n.sub.10 = 1.56873                                                                       ν.sub.10 = 63.16                        r.sub.19 = -19.6489                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 1.0000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        r.sub.21 = ∞                                                                        d.sub.21 = 0.7000                                                 r.sub.22 = ∞                                                                        d.sub.22 = 5.8600                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.23 = ∞                                                                        d.sub.23 = 1.2100                                                 r.sub.24 = ∞                                                                        d.sub.24 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.25 = ∞                                                            aspherical surface coefficient                                                (12th surface)                                                                P = 1.000, A.sub.4 = -0.10430 × 10.sup.-3                               A.sub.6 = -0.49710 × 10.sup.-6, A.sub.8 = 0.20608                       × 10.sup.-8                                                             (18th surface)                                                                P = 1.0000, A.sub.4 = -0.20376 × 10.sup.-3                              A.sub.6 = -0.22521 × 10.sup.-5, A.sub.8 = 0.29150                       × 10.sup.-7                                                             f       6.700          18.383  50.440                                         D.sub.1 0.800          11.933  19.316                                         D.sub.2 13.844         6.422   1.500                                          D.sub.3 4.760          2.510   6.762                                          D.sub.4 3.608          5.858   1.606                                          f.sub.1 /{f.sub.T (f.sub.W ·  f.sub.T).sup.1/2 }.sup.1/2  =          1.104,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.372                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 0.960,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.785                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.1059,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.234                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.064         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.667         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.609,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.478                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub. 36) = 1.216,                         R.sub.41 /R.sub.36 = 1.280                                                    total length of lens system 59.299                                            diameter of front lens component 24.6φ                                    Embodiment 13                                                                 f = 6.700˜50.440,                                                                          F/1.45˜F/2.29                                        2ω = 50.4°˜7.2°                                     r.sub.1 = 55.4246                                                                         d.sub.1 = 1.4000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 27.2103                                                                         d.sub.2 = 5.2000                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = -87.4611                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 20.1075                                                                         d.sub.4 = 3.3000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 55.4501                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 46.3576                                                                         d.sub.6 = 0.9000                                                                          n.sub.4 = 1.60311                                                                        ν.sub.4 = 60.70                         r.sub.7 = 7.6705                                                                          d.sub.7 =  3.3000                                                 r.sub.8 = -10.4549                                                                        d.sub.8 = 0.9000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 9.6357                                                                          d.sub.9 = 2.4000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 44.8278                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.500                                                  r.sub.12 = 10.5254                                                                        d.sub.12 = 5.5403                                                                         n.sub.7 (graded refractive                                                    index lens 1)                                         r.sub.13 = -122.1190                                                                      d.sub.13 = 0.2000                                                 r.sub.14 = 57.2174                                                                        d.sub.14 = 1.2363                                                                         n.sub.8 (graded refractive                                                    index lens 2)                                         r.sub.15 = 10.9471                                                                        d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 16.3464                                                                        d.sub.16 = 3.6384                                                                         n.sub.9 (graded refractive                                                    index lens 3)                                         r.sub.17 = -38.6328                                                                       d.sub.17  = D.sub.4                                                           (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 5.8600                                                                         n.sub.10 = 1.54771                                                                       ν.sub.10 = 62.83                        r.sub.19 = ∞                                                                        d.sub.19 = 1.2100                                                 r.sub.20 = ∞                                                                        d.sub.20 = 0.6000                                                                         n.sub.11 = 1.48749                                                                       ν.sub.11 = 70.20                        r.sub.1 = ∞                                                             graded refractive index lens 1                                                wave length N.sub.0       N.sub.1                                             587.56      1.60311       -0.96088 × 10.sup.-3                          656.28      1.60008       -0.86366 × 10.sup.-3                          486.13      1.61002       -0.86201 × 10.sup.-3                          wave length N.sub.2                                                           587.56      0.13611 × 10.sup.-4                                         656.28      0.15883 × 10.sup.-4                                         486.13      0.17095 × 10.sup.-4                                         graded refractive index lens 2                                                wave length N.sub.0       N.sub.1                                             587.56      1.68893       -0.44201 × 10.sup.-2                          656.28      1.68248       -0.51824 × 10.sup.-2                          486.13      1.70465       -0.52764 × 10.sup.-2                          wave length N.sub. 2                                                          587.56      0.62536 × 10.sup.-4                                         656.28      0.73930 × 10.sup.-4                                         486.13      0.77591 × 10.sup.-4                                         graded refractive index lens 3                                                wave length N.sub.0       N.sub.1                                             587.56      1.60311       -0.18390 × 10.sup.-2                          656.28      1.60008       -0.17437 × 10.sup.-2                          486.13      1.61002       -0.16776 × 10.sup.-2                          wave length N.sub.2                                                           587.56      -0.19369 × 10.sup.-5                                        656.28      -0.29650 × 10.sup.-5                                        486.13      -0.55626 × 10.sup.-5                                        f       6.700          18.383  50.440                                         D.sub.1 0.700          10.328  17.277                                         D.sub.2 18.077         8.449   1.500                                          D.sub.3 4.538          2.475   7.063                                          D.sub.4 4.787          6.849   2.262                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.061,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.408                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.252,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.854                       HH.sub.II III /(f.sub.W ·  f.sub.T).sup.1/2  = -0.1524,              H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.185                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.949         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.864         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2  = 0.579,                  D.sub.FT f.sub.T.sup.2 = 2.776 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.841                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.473,                          R.sub.41 /R.sub.36 = 1.493                                                    total length of lens system 64.965                                            diameter of front lens component 25.5φ                                    Embodiment 14                                                                 f = 6.700˜50.440,                                                                          F/1.45˜F/2.30                                        2ω = 50.4°˜7.2°                                     r.sub.1 = 56.9259                                                                         d.sub.1 = 1.4000                                                                          n.sub. 1 = 1.84666                                                                       ν.sub.1 = 23.78                         r.sub.2 = 27.5385                                                                         d.sub.2 = 5.1000                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = -87.4998                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 20.8150                                                                         d.sub.4 = 3.3000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 63.8668                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 91.6022                                                                         d.sub.6 = 0.9000                                                                          n.sub.4 = 1.60311                                                                        ν.sub.4 = 60.70                         r.sub.7 = 7.8421                                                                          d.sub.7 = 3.2000                                                  r.sub.8 = -10.9528                                                                        d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 9.7328                                                                          d.sub.9 = 2.4000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 57.9526                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.5000                                                 r.sub.12 = 10.6401      n.sub.7 (graded refractive                                        d.sub.12 = 7.2176                                                                         index lens)                                           r.sub.13 = -34.2560                                                                       d.sub.13 = 0.2000                                                 r.sub.14 = -866.5188                                                                      d.sub.14 = 0.9000                                                                         n.sub.8 = 1.84666                                                                        ν.sub.8 = 23.78                         r.sub.15 = 12.4001                                                                        d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 11.5959                                                            (aspherical surface)                                                                      d.sub.16 = 4.0000                                                                         n.sub.9 = 1.48749                                                                        ν.sub.9 = 70.20                         r.sub.17 = -18.0077                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 5.8600                                                                         n.sub.10 = 1.5477                                                                        ν.sub.10 = 62.83                        r.sub.19 = ∞                                                                        d.sub.19 = 1.2100                                                 r.sub.20 = ∞                                                                        d.sub. 20 = 0.6000                                                                        n.sub.11 = 1.48749                                                                       ν.sub.11 = 70.20                        r.sub.21 = ∞                                                            aspherical surface coefficient                                                P = 1.0000, A.sub.4 = -0.19046 × 10.sup.-3                              A.sub.6 = -0.61255 × 10.sup.-5, A.sub.8 = 0.85120                       × 10.sup.-7                                                             graded refractive index lens                                                  wave length N.sub.0       N.sub.1                                             587.56      1.60311       -0.18280 × 10.sup.-2                          656.28      1.60008       -0.18174 × 10.sup.-2                          486.13      1.61002       -0.18543 × 10.sup.-2                          wave length N.sub.2                                                           587.56      -0.14795 × 10.sup.-5                                        656.28      -0.16875 × 10.sup.-5                                        486.13      -0.13249 × 10.sup.-5                                        f       6.700          18.383  50.440                                         D.sub.1 0.700          10.587  17.422                                         D.sub.2 18.222         8.335   1.500                                          D.sub.3 4.424          2.405   7.032                                          D.sub.4 4.870          6.889   2.262                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.061,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup. 1/2  = 0.417                      f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.138,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.824                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.1060,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.239                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.960         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.797         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.670,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.526                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.972,                          R.sub.41 /R.sub.36 = 0.935                                                    total length of lens system 64.956                                            diameter of front lens component 25.0φ                                    Embodiment 15                                                                 f = 6.700˜50.44,                                                                           F/1.44˜F/2.11                                        2ω = 50.4°˜7.2°                                     r.sub.1 = 55.1109                                                                         d.sub.1 = 1.3000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 28.8970                                                                         d.sub.2 = 4.8000                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = -92.8429                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 20.7944                                                                         d.sub.4 = 3.4500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 51.7240                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 100.5677                                                                        d.sub.6 = 0.9000                                                                          n.sub.4 = 1.72000                                                                        ν.sub.4 = 50.25                         r.sub.7 = 9.0549                                                                          d.sub.7 = 3.2000                                                  r.sub.8 = -11.5198                                                                        d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub. 5 = 60.70                        r.sub.9 = 12.5374                                                                         d.sub.9 = 2.0000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 73.5525                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = 14.7025                                                            (aspherical surface)                                                                      d.sub.11 = 3.3000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.12 = -55.8822                                                                       d.sub.12 = 1.0000                                                 r.sub.13 = ∞ (stop)                                                                 d.sub.13 = 1.5000                                                 r.sub.14 = 9.4162                                                                         d.sub.14 = 2.6000                                                                         n.sub.8 = 1.69680                                                                        ν.sub.8 = 55.52                         r.sub.15 = 30.8448                                                                        d.sub.15 = 0.7000                                                 r.sub.16 = -32.9050                                                                       d.sub.16 = 0.8000                                                                         n.sub.9 = 1.84666                                                                        ν.sub.9 = 23.78                         r.sub.17 = 10.4169                                                                        d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 10.1889                                                            (aspherical surface)                                                                      d.sub.18 =  3.6000                                                                        n.sub.10 = 1.56873                                                                       ν.sub.10 = 63.16                        r.sub.19 = -14.9311                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 1.0000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        r.sub.21 = ∞                                                                        d.sub.21 = 5.8600                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.22 = ∞                                                                        d.sub.22 = 1.2100                                                 r.sub.23 = ∞                                                                        d.sub.23 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.24 = ∞                                                            aspherical surface coefficient                                                (11th surface)                                                                P = 1.0000, A.sub.4 = 0.18511 × 10.sup.-4                               A.sub.6 = -0.10252 × 10.sup.-5, A.sub.8 = 0.13963                       × 10.sup.-7                                                             (18th surface)                                                                P = 1.0000, A.sub.4 = -0.37628 × 10.sup.-3                              A.sub.6  = 0.47003 × 10.sup.-6, A.sub.8 = -0.24529                      × 10.sup.-7                                                             f       6.700          18.383  50.44                                          D.sub.1 0.700          10.890  18.161                                         D.sub.2 18.161         7.971   0.700                                          D.sub.3 4.709          2.563   6.507                                          D.sub.4 2.718          4.864   0.920                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.109,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.427                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.088,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.611                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.2627,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.478                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.148         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.669         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.734,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.583                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 0.519,                          R.sub.41 /R.sub.36 = 0.978                                                    total length of lens system 63.025                                            diameter of front lens component 25.7φ                                    Embodiment 16                                                                 f = 6.7˜18.38˜50.44                                               F.sub.NO = 1.85˜2.02˜2.39                                         ω = 25.18˜9.72˜3.57°                                 r.sub.1 = 38.9550                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 22.9987                                                                         d.sub.2 = 4.2500                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = -279.6634                                                                       d.sub.3 = 0.1500                                                  r.sub.4 = 21.3776                                                                         d.sub.4 = 3.2500                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 94.2597                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 204.4263                                                                        d.sub.6 = 0.9000                                                                          n.sub.4 = 1.69680                                                                        ν.sub.4 = 55.52                         r.sub.7 = 7.7743                                                                          d.sub.7 = 2.8000                                                  r.sub.8 = -12.6764                                                                        d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 11.2751                                                                         d.sub.9 = 2.0000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = 68.6575                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞](stop)                                                                 d.sub.11 = 1.4000                                                 r.sub.12 = 6.5200                                                             (aspherical surface)                                                                      d.sub.12 = 3.6000                                                                         n.sub.7 = 1.69680                                                                        ν.sub.7 = 55.52                         r.sub.13 = 173.1581                                                                       d.sub.13 = 0.1500                                                 r.sub.14 = 15.0584                                                                        d.sub.14 = 0.8000                                                                         n.sub.8 = 1.84666                                                                        ν.sub.8 = 23.78                         r.sub.15 = 5.6605                                                                         d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 10.5785                                                                        d.sub.16 = 2.5500                                                                         n.sub.9 = 1.58913                                                                        ν.sub.9 = 60.97                         (aspherical surface)                                                          r.sub.17 = -26.8865                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 1.6000                                                                         n.sub.10 = 1.51633                                                                       ν.sub.10 = 64.15                        r.sub.19 = ∞                                                                        d.sub.19 = 4.4000                                                                         n.sub.11 = 1.54771                                                                       ν.sub.11 = 62.83                        r.sub.20 = ∞                                                                        d.sub.20 = 0.5000                                                 r.sub.21 = ∞                                                                        d.sub.21 = 0.6000                                                                         n.sub.12 = 1.48749                                                                       ν.sub.12 = 70.20                        r.sub.22 = ∞                                                                        d.sub.22 = 1.1600                                                 r.sub.23 = ∞                                                            f       6.7            18.38   50.44                                          D.sub.1 0.700          9.744   16.493                                         D.sub.2 17.193         8.149   1.400                                          D.sub.3 4.719          2.984   8.574                                          D.sub.4 5.356          7.091   1.500                                          aspherical surface coefficient                                                (12th surface)                                                                P = 1, A.sub.4 = -0.30923 × 10.sup.-3                                   A.sub.6 = -0.69943 × 10.sup.-6, A.sub.8 = -0.24097                      × 10.sup.-6                                                             (16th surface)                                                                P = 1, A.sub.4 = -0.14135 × 10.sup.-3                                   A.sub.6 = -0.51072 × 10.sup.-5, A.sub.8 = 0.12180                       × 10.sup.-6                                                             f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.990,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.405                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.280,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.719                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = - 0.0259,              H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.355                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.509         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.364         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.386,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -1.078                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 2.205,                          R.sub.41 /R.sub.36 = 1.869                                                    Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.004 (y                     = 0.182y.sub.1)                                                               Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.146(y = 0.437y.sub.1)      total length of lens system 57.788                                            diameter of front lens component 22.5φ                                    Embodiment 17                                                                 f = 6.7˜18.38˜50.44                                               F.sub. NO = 1.85˜2.04˜2.35                                        ω = 25.18˜9.72˜3.57°                                 r.sub.1 = 26.3774                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 17.7731                                                                         d.sub.2 = 4.9000                                                                          n.sub.2 = 1.56873                                                                        ν.sub.2 = 63.16                         r.sub.3 = 657.1990                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 22.1232                                                                         d.sub.4 = 2.9000                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 71.7507                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub.6 = 100.2516                                                                        d.sub.6 = 0.9000                                                                          n.sub.4 = 1.83400                                                                        ν.sub.4 = 37.16                         r.sub.7 = 6.6206                                                                          d.sub.7 = 2.5000                                                  r.sub.8 = -8.8402                                                                         d.sub.8 = 0.8000                                                                          n.sub.5 = 1.62230                                                                        ν.sub.5 = 53.20                         r.sub.9 =  9.8650                                                                         d.sub.9 = 2.4000                                                                          n.sub.6 = 1.84666                                                                        ν.sub.6 = 23.78                         r.sub.10 = -51.6671                                                                       d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = 14.2950                                                            (aspherical surface)                                                                      d.sub.11 = 2.2000                                                                         n.sub.7 = 1.58913                                                                        ν.sub.7 = 60.97                         r.sub.12 = -43.2848                                                                       d.sub.12 = 0.6000                                                 r.sub.13 = ∞ (stop)                                                                 d.sub.13 = 1.4000                                                 r.sub.14 = 10.4076                                                                        d.sub.14 = 3.0000                                                                         n.sub.8 = 1.62374                                                                        ν.sub.8 = 47.10                         r.sub.15 = -24.0926                                                                       d.sub.15 = 0.1500                                                 r.sub.16 = 71.1257                                                                        d.sub.16 = 0.8000                                                                         n.sub.9 = 1.84666                                                                        ν.sub.9 = 23.78                         r.sub.17 = 7.0558                                                                         d.sub.17 = D.sub.3                                                            (variable)                                                        r.sub.18 = 10.5860                                                            (aspherical surface)                                                                      d.sub.18 = 2.2000                                                                         n.sub.10 = 1.58913                                                                       ν.sub. 10 = 60.97                       r.sub.19 = -52.7672                                                                       d.sub.19 = D.sub.4                                                            (variable)                                                        r.sub.20 = ∞                                                                        d.sub.20 = 1.6000                                                                         n.sub.11 = 1.51633                                                                       ν.sub.11 = 64.15                        r.sub.21 = ∞                                                                        d.sub.21 = 4.4000                                                                         n.sub.12 = 1.54771                                                                       ν.sub.12 = 62.83                        r.sub.22 = ∞                                                                        d.sub.22 = 0.5000                                                 r.sub.23 = ∞                                                                        d.sub.23 = 0.6000                                                                         n.sub.13 = 1.48749                                                                       ν.sub.13 = 70.20                        r.sub.24 = ∞                                                                        d.sub.24 = 1.1600                                                 r.sub.25 = ∞                                                            f       6.7            18.38   50.44                                          D.sub.1 0.700          9.559   15.671                                         D.sub.2 15.571         6.713   0.600                                          D.sub.3 5.966          3.317   7.925                                          D.sub.4 3.459          6.108   1.500                                          aspherical surface coefficient                                                (11th surface)                                                                P = 1, A.sub.4 = -0.18200 × 10.sup.-3                                   A.sub.6 = -0.23816 × 10.sup.-5 , A.sub.8 = 0.15287                      × 10.sup.-7                                                             (18th surface)                                                                P = 1, A.sub.4 = -0.45037 × 10.sup.-4                                   A.sub.6 = -0.82357 × 10.sup.-5, A.sub.8 = 0.24085                       × 10.sup.-6                                                             f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           0.965,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.363                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 0.908,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.825                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.0618,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.196                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 1.320         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2   = 0.453        D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.563,                   D.sub.FT f.sub.T.sup.2 = 4.371 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.503                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 1.220,                          R.sub.41 /R.sub.36 = 1.500                                                    Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.002(y = 0.182y.sub.1)      Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.079(y = 0.437y.sub.1)      total length of lens system 57.767                                            diameter of front lens component 22.3φ                                    Embodiment 18                                                                 f = 6.7˜18.38˜50.44                                               F.sub.NO = 1.85˜1.99˜2.39                                         ω = 25.18˜9.72˜3.57°                                 r.sub.1 = 19.6985                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.84666                                                                        ν.sub.1 = 23.78                         r.sub.2 = 13.7089                                                                         d.sub.2  = 0.0900                                                 r.sub.3 = 13.8901                                                                         d.sub.3 = 6.2000                                                                          n.sub.2 = 1.69680                                                                        ν.sub.2 = 55.52                         r.sub.4 = 1092.6801                                                           (aspherical surface)                                                                      d.sub.4 = D.sub.1                                                             (variable)                                                        r.sub.5 = 46.5765                                                                         d.sub.5 = 0.9000                                                                          n.sub.3 = 1.77250                                                                        ν.sub.3 = 49.66                         r.sub.6 = 5.8624                                                                          d.sub.6 = 2.9700                                                  r.sub.7 = -16.4818                                                                        d.sub.7 = 0.8000                                                                          n.sub.4 = 1.60311                                                                        ν.sub.4 = 60.70                         r.sub.8 = 19.2213                                                                         d.sub.8 = 0.1500                                                  r.sub.9 = 11.9035                                                                         d.sub.9 = 2.0000                                                                          n.sub.5 = 1.84666                                                                        ν.sub.5 = 23.78                         r.sub.10 = 61.8455                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.4000                                                 r.sub.12 = 6.7400                                                             (aspherical surface)                                                                      d.sub.12 = 4.0000                                                                         n.sub.6 = 1.58913                                                                        ν.sub.6 = 60.97                         r.sub.13 = -47.9719                                                                       d.sub.13 = 0.1500                                                 r.sub.14 = 13.2398                                                                        d.sub.14 = 0.8000                                                                         n.sub.7 = 1.84666                                                                        ν.sub.7 = 23.78                         r.sub.15 = 5.7647                                                                         d.sub.15 = D.sub.3                                                            (variable)                                                        r.sub.16 = 10.3940                                                            (aspherical surface)                                                                      d.sub.16 = 2.8000                                                                         n.sub.8 = 1.58913                                                                        ν.sub.8 = 60.97                         r.sub.17 = -41.4945                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 1.6000                                                                         n.sub.9 = 1.51633                                                                        ν.sub.9 = 64.15                         r.sub.19 = ∞                                                                        d.sub.19 = 4.4000                                                                         n.sub.10 = 1.54771                                                                       ν.sub.10 = 62.83                        r.sub.20 = ∞                                                                        d.sub.20 = 0.5000                                                 r.sub.21 = ∞                                                                        d.sub.21 = 0.6000                                                                         n.sub.11 = 1.48749                                                                       ν.sub.11 = 70.20                        r.sub.22 = ∞                                                                        d.sub.22 = 1.1600                                                 r.sub.23 = ∞                                                            f       6.7            18.38   50.44                                          D.sub.1 0.600          10.393  17.462                                         D.sub.2 17.862         8.069   1.000                                          D.sub.3 4.630          2.982   8.312                                          D.sub.4 5.182          6.830   1.500                                          aspherical surface coefficient                                                (4th surface)                                                                 P = 1, A.sub.4 = 0.75640 × 10.sup.-5                                    A.sub.6 = 0.13214 × 10.sup.-7, A.sub.8 = -0.23383                       × 10.sup.-9                                                             (12th surface)                                                                P = 1, A.sub.4 = -0.34910 × 10.sup.-3                                   A.sub.6 = -0.12936 × 10.sup.-5, A.sub.8 = -0.19996                      × 10.sup.-6                                                             (16th surface)                                                                P = 1, A.sub.4 = -0.22649 × 10.sup.-4                                   A.sub.6 = -0.77421 × 10.sup.-5, A.sub.8 = 0.25529                       × 10.sup.-6                                                             f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup. 1/2 }.sup.1/2  =          1.051,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.433                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 1.271,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.783                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = -0.0651,               H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.306                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.622         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.370         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.422,                   D.sub.FT f.sub.T.sup.2 = 3.267 × 10.sup.-3                              (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.754                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) =  2.542,                         R.sub.41 /R.sub.36 = 1.803                                                    Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.004(y = 0.182y.sub.1)      Δx/(f.sub.W · f.sub.T).sup.1/2  = 0.160(y = 0.437y.sub.1)      total length of lens system 57.706                                            diameter of front lens component 21.8φ                                    Embodiment 19                                                                 f = 6.5˜52   F/1.8˜F/2.4                                          2ω = 50.4°˜7.2°                                     r.sub.1 = 43.7901                                                                         d.sub.1 = 1.2000                                                                          n.sub.1 = 1.80518                                                                        ν.sub.1 = 25.43                         r.sub.2 = 23.2327                                                                         d.sub.2 = 6.1700                                                                          n.sub.2 = 1.60311                                                                        ν.sub.2 = 60.70                         r.sub.3 = -96.6864                                                                        d.sub.3 = 0.1500                                                  r.sub.4 = 18.6501                                                                         d.sub.4 = 2.5900                                                                          n.sub.3 = 1.60311                                                                        ν.sub.3 = 60.70                         r.sub.5 = 31.3590                                                                         d.sub.5 = D.sub.1                                                             (variable)                                                        r.sub. 6 = 27.2301                                                                        d.sub.6 = 0.9000                                                                          n.sub.4 = 1.65844                                                                        ν.sub.4 = 50.86                         r.sub.7 = 6.9714                                                                          d.sub.7 = 3.5000                                                  r.sub.8 = -9.1811                                                                         d.sub.8 = 0.8000                                                                          n.sub.5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = 9.1811                                                                          d.sub.9 = 2.3000                                                                          n.sub.6 = 1.80518                                                                        ν.sub.6 = 25.43                         r.sub.10 = 65.7228                                                                        d.sub.10 = D.sub.2                                                            (variable)                                                        r.sub.11 = ∞ (stop)                                                                 d.sub.11 = 1.4000                                                 r.sub.12 = 7.3212                                                             (aspherical surface)                                                                      d.sub.12 = 5.4530                                                                         n.sub.7 = 1.58913                                                                        ν.sub.7 = 60.97                         r.sub.13 = -18.0242                                                                       d.sub.13 = 0.1500                                                 r.sub.14 = 11.8864                                                                        d.sub.14 = 0.8000                                                                         n.sub.8 = 1.84666                                                                        ν.sub.8 = 23.78                         r.sub.15 = 5.6861                                                                         d.sub.15  = D.sub.3                                                           (variable)                                                        r.sub.16 = 9.4173                                                                         d.sub.16 = 2.7000                                                                         n.sub.9 = 1.56873                                                                        ν.sub.9 = 63.16                         r.sub.17 = 297.2498                                                                       d.sub.17 = D.sub.4                                                            (variable)                                                        r.sub.18 = ∞                                                                        d.sub.18 = 1.6000                                                                         n.sub.10 = 1.51633                                                                       ν.sub.10 = 64.15                        r.sub.19 = ∞                                                                        d.sub.19 = 4.4000                                                                         n.sub.11 = 1.54771                                                                       ν.sub.11 = 62.83                        r.sub.20 = ∞                                                                        d.sub.20 = 0.5000                                                 r.sub.21 = ∞                                                                        d.sub.21 = 0.6000                                                                         n.sub.12 = 1.48749                                                                       ν.sub.12 = 70.20                        r.sub.22 = ∞                                                            aspherical surface coefficient                                                P = 1, A.sub.4 = -0.44224 × 10.sup.-3                                   A.sub.6 = -0.17987 × 10.sup.-5, A.sub.8 = -0.11666                      × 10.sup.-6                                                             f       6.5             18.4   52                                             D.sub.1 1.000          10.876  17.778                                         D.sub.2 17.978         8.103   1.200                                          D.sub.3 6.530          3.723   7.277                                          D.sub.4 2.747          5.555   2.000                                          f.sub.1 /{f.sub.T (f.sub.W · f.sub.T).sup.1/2 }.sup.1/2  =           1.110,                                                                        f.sub.II /(f.sub.W · f.sub.T).sup.1/2  = 0.392                       f.sub.III /(f.sub.w · f.sub.T).sup.1/2  = 0.921,                     f.sub.IV /(f.sub.W · f.sub.T).sup.1/2  = 0.927                       HH.sub.II III /(f.sub.W · f.sub.T).sup.1/2  = 0.131,                 H.sub.III /(f.sub.W · f.sub.T).sup.1/2  = -0.189                     R.sub.31 /(N.sub.31 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.676         R.sub.36 /(N.sub.33 - 1)(f.sub.W · f.sub.T).sup.1/2  = 0.365         D.sub.III IV /(f.sub.W · f.sub.T).sup.1/2 = 0.495,                   D.sub.FT f.sub.T.sup.2 = 2.860 × 10.sup.- 3                             (R.sub.31 + R.sub.32)/(R.sub.31 - R.sub.32) = -0.422                          (R.sub.35 + R.sub.36)/(R.sub.35 - R.sub.36) = 2.834,                          R.sub.41 /R.sub.36 = 1.656                                                    total length of lens system 62.430                                            diameter of front lens component 26.4φ                                    ______________________________________                                         wherein the reference symbols r.sub.1, r.sub.2, . . . represent radii of      curvature on the surfaces of the respective lens elements, the reference      symbols d.sub.1, d.sub.2, . . . designate thicknesses of the respective       lens elements and airspaces reserved therebetween, the reference symbols      n.sub.1, n.sub.2, . . . denote refractive indices of the respective lens      elements, and the reference symbols ν.sub.1, ν.sub.2, . . .             represent Abbe's numbers of the respective lens elements.                

The Embodiment 1 has the composition illustrated in FIG. 1, wherein thethird lens unit consists of a positive lens element and a negative lenselement, and the fourth lens element is composed of a positive lenselement. Further, the object side surface (r₁₂) of the third lens unitand the object side surface (r₁₆) of the fourth lens unit are designedas aspherical surfaces respectively.

The Embodiment 2 has the composition illustrated in FIG. 2, wherein thethird lens unit consists of three positive lens elements and a negativelens element, whereas the fourth lens unit is composed of a positivelens element. Further, the object side surface (r₂₀) of the fourth lensunit is designed as an aspherical surface.

The Embodiment 3 has the composition shown in FIG. 3, wherein the thirdlens unit consists of a positive lens element, a negative lens elementand a positive lens element, whereas the fourth lens unit is composed ofa positive lens element. The object side surface (r₁₈) of the fourthlens unit is designed as an aspherical surface.

The Embodiment 4 has the composition shown in FIG. 4, wherein the thridlens unit consists of two positive lens elements and a negative lenselement, whereas the fourth lens unit is composed of a positive lenselement. The object side surface (r₁₈) of the fourth lens unit isdesigned as an aspherical surface.

The Embodiment 5 has the composition presented in FIG. 5, wherein thethird lens unit consists of two positive lens elements and a negativelens element, whereas the fourth lens unit is composed of two positivelens elements. The object side surface (r₂₀) of the positive lenselement arranged on the image side in the fourth lens unit is designedas an aspherical surface.

The Embodiment 6 has the composition illustrated in FIG. 6, wherein thethird lens unit consists of two positive lens elements and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit is composed of a positive lens element. Theobject side surface (r₁₂) of the third lens unit and the object sidesurface (r₁₈) of the fourth lens unit are designed as aspherical surfacehaving curvature which is lowered as the portions of said asphericalsurfaces are farther from the optical axis.

The Embodiment 7 has the composition illustrated in FIG. 7, wherein thethird lens unit consists of two positive lens elements and a negativelens element, whereas the fourth lens unit is composed of a positivelens element. The object side surface (r₁₂) of the third lens unit andthe object side surface (r₁₈) of the fourth lens unit are designed asaspherical surfaces respectively.

In the Embodiment 7, the first lens unit and the second lens unit aremoved in the directions reverse to each other for variation of focallength.

The Embodiment 8 has the composition shown in FIG. 8, wherein the thirdlens unit consists of a positive lens element and a negative lenselement having a strongly concave surface on the image side, whereas thefourth lens unit is composed of a positive lens element. The object sidesurface (r₁₂) of the third lens unit and the object side surface (r₁₈)of the fourth lens unit are designed as aspherical surfaces havingcurvature which is lowered as the portions of said aspherical surfacesare farther from the optical axis.

The Embodiment 9 has the composition illustrated in FIG. 9, wherein thethird lens unit consists of a positive lens element and a negative lenselement having a strongly concave surface on the image side, whereas thefourth lens unit is composed of a positive lens element. The object sidesurface (r₁₂) of the third lens unit and the object side surface (r₁₆)of the fourth lens unit are designed as aspherical surfaces havingcurvature which is lowered as the portions of said aspherical surfacesare farther from the optical axis.

The Embodiment 10 has the composition illustrated in FIG. 10, whereinthe third lens unit consists of a positive lens element and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit is composed of a positive lens element. Theobject side surface (r₁₂) of the third lens unit and the object sidesurface (r₁₆) of the fourth lens unit are aspherical surfaces havingcurvature which is lowered as the portions of said aspherical surfacesare farther from the optical axis.

In the Embodiment 10, the first lens unit and the second lens unit aremoved in the directions reverse to each other for varying focal lengthof the vari-focal lens system.

The Embodiment 11 has the composition shown in FIG. 11, wherein thethird lens unit consists of two positive lens elements and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit is composed of a positive lens element. Theobject side surface (r₁₁) of the third lens unit and the object sidesurface (r₁₈) of the fourth lens unit are aspherical surfaces havingcurvature which is lowered as the portions of said aspherical surfaceare farther from the optical axis.

The Embodiment 12 has the composition visualized in FIG. 12, wherein thethird lens unit consists of two positive lens elements and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit is composed of a positive lens element. Theobject side surface (r₁₂) of the third lens unit and the object sidesurface (r₁₈) of the fourth lens unit are aspherical surfacesrespectively.

The Embodiment 13 has the composition illustrated in FIG. 13, whereinthe third lens unit is composed of a positive lens element and anegative lens element having a strongly concave surface on the imageside, whereas the fourth lens unit consists of a positive lens element.In the Embodiment 13, all the lens elements arranged in the third lensunit and the fourth lens unit are made of an unhomogenous medium havinga refractive index which is lowered as the portions of said lenselements are farther from the optical axis.

The Embodiment 14 has the composition visualized in FIG. 14, wherein thethird lens unit is composed of a positive lens element and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit consists of a positive lens element. Thepositive lens element arranged on the object side in the third lens unitis made of an unhomogenous medium having refractive index which islowered as the portions of said lens element are farther from theoptical axis.

The Embodiment 15 has the composition illustrated in FIG. 15 wherein thethird lens unit is composed of a positive lens element and a negativelens element having a strongly concave surface on the image side,whereas the fourth lens unit consists of a positive lens element. Theobject side surface (r₁₁) of the third lens unit and the object sidesurface (r₁₈) of the fourth lens unit are designed as asphericalsurfaces having curvature which is lowered as the portions of saidaspherical surfaces are farther from the optical axis.

The Embodiment 16 has the composition shown in FIG. 16, wherein thethird lens unit consists of a positive lens element and a negative lenselement, whereas the fourth lens unit is composed of a single positivelens element. The object side surface (r₁₂) of the third lens unit andthe object side surface (r₂₂) of the fourth lens unit are asphericalsurfaces.

The Embodiment 17 has the composition illustrated in FIG. 17, whereinthe third lens unit consists of two positive lens elements and anegative lens element, whereas the fourth lens unit is composed of apositive lens element. The object side surface (r₁₁) of the third lensunit and the object side surface (r₁₈) of the fourth lens unit areaspherical surfaces.

The Embodiment 18 has the composition shown in FIG. 18, wherein thethird lens unit consists of a positive lens element and a negative lenselement, whereas the fourth lens unit is composed of a positive lenselement. The object side surface (r₁₂) of the third lens unit and theobject side surface (r₁₆) of the fourth lens unit are asphericalsurfaces.

The Embodiment 19 has the composition visualized in FIG. 19, wherein thethird lens unit consists of a positive lens element and a negative lenselement, whereas the fourth lens unit is composed of a positive lenselement. The object side surface (r₁₂) of the third lens unit is anaspherical surface.

When the direction of the optical axis is taken as the x axis and thedirection perpendicular to the optical axis is taken as the y axis, theshapes of the aspherical surfaces used in the embodiments are expressedby the following formula: ##EQU6## wherein the reference symbol rrepresents the radius of curvature on an aspherical surface of interestas measured in the vicinity of the optical axis, the reference symbol Pdenotes conic constant and the reference symbol A_(2i) designates theaspherical surface coefficient.

Further, refractive index distribution of the graded refractive indexlens used in the Embodiments is expressed by the following formula:

    n(r)=N.sub.0 +N.sub.1 r.sup.2 +N.sub.2 r.sup.4 +N.sub.3 r.sup.6 +. . .

wherein the reference symbol N₀ represents refractive index of theportion located on the optical axis, the reference symbol r designatesdistance as measured from the optical axis in the radial direction, andthe reference symbols N₁, N₂, . . . denote the refractive indexdistribution coefficients.

We claim:
 1. A vari-focal lens system comprising, in order from theobject side,a vari-focal subsystem comprising a first lens unit having apositive refractive power and a second lens unit having a negativerefractive power; and an imaging subsystem comprising a third lens unithaving a positive refractive power, and a fourth lens unit having apositive refractive power and being movable during the variation oflocal length mainly for correcting deviation of the image position; saidthird lens unit consisting of two to four lens components including apositive lens component on the object side and having a convex surfaceon the object side, and a negative lens component having a concavesurface on the image side, said fourth lens unit consisting of two or asmaller number of positive lens components, and at least one of the lenssurfaces in said imaging subsystem being an aspherical surface havingrefractive power weakened as the portions of said aspherical surface arefarther from the optical axis.
 2. A vari-focal lens system according toclaim 1 adapted to be focused by moving said fourth lens unit along theoptical axis.
 3. A vari-focal lens system according to claim 1satisfying the conditions (1), (2) and (3) listed below:

    0.55<f.sub.I /{f.sub.T (f.sub.W ·f.sub.T).sup.1/2 }.sup.1/2 <1.35 (1)

    0.4<f.sub.III /(f.sub.W ·f.sub.T).sup.1/2 2.5     (2)

    -0.5<HH.sub.II-III /(f.sub.W ·f.sub.T).sup.1/2 <0.25 (3)

wherein the reference symbols f_(W) and f_(T) represent the focallengths of the vari-focal lens system as a whole at the wide positionand the tele position respectively, the reference symbols f_(I) andf_(III) designate the focal lengths of the first lens unit and the thirdlens unit respectively, and the reference symbol HH_(II-III) denotes thedistance as measured between the principal points of the second lensunit and the third lens unit at the tele position.
 4. A vari-focal lenssystem according to claim 3 wherein said third lens unit comprises anegative lens component arranged on the image side.
 5. A vari-focal lenssystem according to claim 4 wherein said third lens unit and said fourthlens unit satisfy the conditions (4), (5) and (6) mentioned below:

    0.3<R.sub.31 /(N.sub.31 -1)(f.sub.W ·f.sub.T).sup.1/2 <2.0 (4)

    0.2<R.sub.36 /(N.sub.33 -1)(f.sub.W ·f.sub.T).sup.1/2 <1.6 (5)

    0.25<(D.sub.III +D.sub.IV)/(f.sub.W ·f.sub.T).sup.1/2 1.5 (6)

wherein the reference symbols R₃₁ and R₃₆ represent the radii ofcurvature on the object side surface and the image side surfacerespectively of said third lens unit, the reference symbols D_(III) andD_(IV) designate the total thickness of the third lens unit and that ofthe fourth lens unit respectively, and the reference symbols N₃₁ and N₃₃denote the refractive indices of the lens component arranged on theobject side and the lens component arranged on the image siderespectively in the third lens unit.
 6. A vari-focal lens systemaccording to claim 4 wherein said third lens unit and said fourth lensunit satisfy the conditions (7) through (10) mentioned below:

    1.0×10.sup.-3 <D.sub.FT /f.sub.T .sup.2 <7.0×10.sup.-3 ( 7)

    -1.8<(R.sub.31 +R.sub.32)/(R.sub.31 -R.sub.32)<-0.1        (8)

    0.2<(R.sub.35 +R.sub.36)/(R.sub.35 -R.sub.36)<3.5          (9)

    0.6<R.sub.41 /R.sub.36 <2.4                                (10)

wherein the reference symbols R₃₁ and R₃₂ represent the radii ofcurvature on the object side surface and the image side surfacerespectively of the lens component arranged on the object side in thethird lens unit, the reference symbols R₃₅ and R₃₆ designate the radiiof curvature on the object side surface and the image side surfacerespectively of the lens component arranged on the image side in thethird lens unit, the reference symbol R₄₁ denotes the radius ofcurvature on the object side surface of the fourth lens unit, and thereference symbol D_(FT) represents the distance as measured between thethird lens unit and the fourth lens unit at the tele position.
 7. Avari-focal lens system according to claim 4 wherein said asphericalsurface satisfies the following conditions (11) and (12): ##EQU7##wherein the reference symbol Δx represents the departure of saidaspherical surface from the reference sphere thereof, the referencesymbol y designates the distance as measured from the optical axis to aportion of interest on said aspherical surface and the reference symboly₁ denotes a value expressed as ##EQU8## (the reference symbol Frepresents the F number of the vari-focal lens system at the wideposition).
 8. A vari-focal lens system according to claim 1 wherein saidthird lens unit consist of, in the order from the object side, apositive lens component having a convex surface on the object side, twopositive lens components and a negative lens component having a concavesurface on the image side, and said fourth lens unit consists of apositive lens component.
 9. A vari-focal lens system according to claim1 wherein said third lens unit consists of, in the order from the objectside, a positive lens component having a convex surface on the objectside, a positive lens component and a negative lens component having aconcave surface on the image side, and said fourth lens unit consists ofa positive lens component having an aspherical surface.
 10. A vari-focallens system according to claim 1 wherein said third lens unit consistsof, in the order from the object side, a positive lens component havinga convex object side surface designed as an aspherical surface havingcurvature lowered as the portions of said aspherical surface are fartherfrom the optical axis, a positive lens component and a negative lenscomponent having a concave surface on the image side, and said fourthlens unit consists of a positive lens component.
 11. A vari-focal lenssystem according to claim 1 wherein said third lens unit consists of, inthe order from the object side, a positive lens component having aconvex object side surface designed as an aspherical surface havingcurvature lowered as the portions of said aspherical surface are fartherfrom the optical axis and a negative lens component having a concavesurface on the image side, and said fourth lens unit consists of apositive lens component.
 12. A vari-focal lens system according to claim1 wherein said third lens unit consists of, in the order from the objectside, a positive lens component having a convex surface on the objectside, a negative lens component having a concave surface on the imageside and a positive lens component, and said fourth lens unit consistsof a positive lens component having an aspherical surface.
 13. Avari-focal lens system according to claim 1 wherein said third lens unitconsists of, in the order from the object side, a positive lenscomponent having a convex surface on the object side, a positive lenscomponent and a negative lens component having a concave surface on theimage side, and said fourth lens unit consists of two positive lenscomponents, and said imaging subsystem comprises an aspherical surface.14. A vari-focal lens system according to claim 1 satisfying thefollowing condition (1'): ##EQU9## wherein the reference symbols f_(W)and f_(T) represent the focal lengths of the vari-focal lens system as awhole at the wide position and the tele position respectively, and thereference symbol f_(II) designates the focal length of said second lensunit.
 15. A vari-focal lens system according to claim 1 satisfying thefollowing condition (2'): ##EQU10## wherein the reference symbols f_(W)and f_(T) represent the focal lengths of the vari-focal lens system as awhole at the wide position and tele position respectively, and thereference symbol f_(IV) deisgnates the focal length of said fourth lensunit.
 16. A vari-focal lens system according to claim 1 satisfying thefollowing condition (3'): ##EQU11## wherein the reference symbols f_(W)and f_(T) represent the focal lengths of the vari-focal lens system as awhole at the wide position and the tele position respectively, and thereference symbol HH_(II-III) designates the distance as measured betweenthe principal points of the second lens unit and the third lens unit atthe tele position.
 17. A vari-focal lens system comprising, in the orderfrom the object side,a first lens unit having a positive refractivepower and kept stationary during variation of focal length; a secondlens unit having a negative refractive power, movable during thevariation of focal length and having a vari-focal function; a third lensunit having a positive refractive power and kept stationary during thevariation of focal length; and a fourth lens unit having a positiverefractive power, movable during the variation of focal length andhaving a function mainly to correct deviation of image position; saidthird lens unit consisting of two to four lens components including apositive lens component arranged on the object side and having a convexsurface on the object side, and a negative lens component, said fourthlens unit consisting of two or a smaller number of positive lenscomponents, and said fourth lens unit comprising at least one asphericalsurface having refractive power weakened as the portions of saidaspherical surface are farther from the optical axis.
 18. A vari-focallens system according to claim 17 wherein said fourth lens unitsatisfies the following condition:

    -1.8<(R.sub.1 +R.sub.2)/(R.sub.1 -R.sub.2)<-0.1

wherein the reference symbols R₁ and R₂ represent the radii of curvatureon the object side surface and the image side surface respectively ofthe lens component having said aspherical surface in the fourth lensunit.
 19. A vari-focal lens system according to claim 17 wherein saidnegative lens component is arranged on the image side of said positivelens component.
 20. A vari-focal lens system according to claim 17wherein the two lens component arranged on the image side in said thirdlens unit are a positive lens component having a strongly convex surfaceon the object side and a negative lens component having a stronglyconcave surface on the image side.